Composite spinneret, multicomponent fiber, and method of producing multicomponent fiber

ABSTRACT

A multicomponent fiber includes a sea component and an island component, wherein in cross-section observation of the multicomponent fiber, the multicomponent fiber includes a sea-island region with the plurality of island components arranged in the sea component; and one or more sea component regions formed only of the sea component between the sea-island region, and a width (H) of the sea component region is larger than a maximum value of a distance (W) between island components existing in the sea-island region and neighboring each other.

TECHNICAL FIELD

This disclosure relates to a composite spinneret that discharges a composite polymer flow composed of two or more polymers, a multicomponent fiber obtained by performing melt spinning by a composite spinning machine using the composite spinneret, and a method of producing a multicomponent fiber.

BACKGROUND

By combining two or more polymers, performance which is not sufficient with a single-component polymer has been complemented, and various multicomponent fibers having novel functions have been developed with diversification of applications.

A sea-island multicomponent fiber, one of multicomponent fibers, is a fiber in which in cross-section observation, two or more polymers having different compositions are phase-separated, some kind of polymer is dispersed in another polymer, and the former polymer looks like islands while the latter polymer looks like sea. Hereinafter, the former polymer is referred to as an “island polymer,” and the latter polymer is referred to as a “sea polymer” in some cases.

After sea-island multicomponent fibers are produced by performing melt-spinning, a sea polymer as an easily soluble component is removed to leave only an island polymer as a hardly soluble component so that ultrafine fibers with each single fiber having a thread diameter in a nanometer order can be obtained. In applications of clothes, those fibers can be applied to artificial leathers and new-touch textiles since soft touch and fineness that cannot be achieved with common fibers are realized. Further, those fibers can be expanded to applications of sports wear required to have windbreaking performance and water repellency as high-density fabrics because they have reduced fiber gaps. In applications of industrial materials, those fibers can be applied to high-performance filters in view of increasing the specific surface area to improve dust collecting performance, and to wiping cloths and precise polishing cloths for precision equipment in view of wiping out contaminants with ultrafine fibers entering very small grooves.

Generally, a method of forming a composite polymer flow in a composite spinneret, and producing a multicomponent fiber therefrom is referred to as a composite spinning method, and a method of producing a multicomponent fiber by melting and kneading polymers is referred to as a polymer alloy method.

In the polymer alloy method, ultrafine fibers can be produced similarly to the composite spinning method, but control of the fiber diameter is limited so that it is difficult to obtain uniform ultrafine fibers. On the other hand, the composite spinning method is capable of forming a composite polymer flow composed of two or more polymers in a composite spinneret, and precisely controlling a composite structure. Therefore, the composite spinning method is superior to the polymer alloy method in that a thread cross-section form with high accuracy can be uniformly formed.

To make it possible to stably control the thread cross-section form in the composite spinning method, a composite spinneret technique is important. Therefore, various proposals have been heretofore made.

Composite spinneret techniques related to sea-island multicomponent fibers may be classified broadly into two techniques: a pipe type spinneret technique and a distribution type spinneret technique.

A typical example of the pipe type spinneret is disclosed in Japanese Patent Laid-open Publication No. 2001-192924. FIG. 15 shows a partial enlarged longitudinal sectional view of the composite spinneret disclosed in Japanese Patent Laid-open Publication No. 2001-192924. In the drawings, explanations may be omitted when there exists a member with the same reference symbol as that corresponding to a drawing that has already been explained.

The pipe type spinneret shown in FIG. 15 includes a distribution device 1 provided with sea polymer introduction channels 21, an island polymer introduction channel 22, pipes 20 and a sea polymer distribution chamber 23; a nozzle plate 2 provided with composite polymer discharge holes 15; and a flow contraction plate 3 provided with a spinneret discharge hole 6.

In that spinneret, a sea polymer as an easily soluble component is guided from the sea polymer introduction channels 21 to the sea polymer distribution chamber 23, and fills the outer periphery of each of the pipes 20. On the other hand, an island polymer as a hardly soluble component is guided from the island polymer introduction channel 22 to the pipes 20, and discharged from the pipes 20. The island polymer discharged from the pipes 20 is put in the sea polymer filling the sea polymer distribution chamber 23 so that a composite polymer flow with the island polymer covered with the sea polymer is formed. Thereafter, the composite polymer flow merges with another composite polymer flow by passing through the composite polymer discharge holes 15, and is discharged from the spinneret discharge hole 6 to form a multicomponent fiber having a sea-island cross section.

In a pipe type spinneret as described above, when the number of the pipes 20 per unit area is increased to a working limit, the number of island components increases, the number of ultrafine fibers after sea removal can be increased, and the fiber diameter of the ultrafine fiber can be reduced on the cross section of the sea-island multicomponent fiber. However, when the number of the pipes 20 is increased, the distance between pipes decreases so that the sea polymer cannot infiltrate into the central part of the pipes 20, and thus distributivity of the sea polymer is deteriorated. Therefore, in some portions, the island polymer is not covered with the sea polymer, and particularly when spinning is performed at a high island polymer ratio, island polymers may merge with each other. To solve this problem, the arrangement of the pipes 20 should be optimized to improve distributivity of the sea polymer, and a typical example of the solution is disclosed in each of Japanese Patent Laid-open Publication No. 2009-91680 and National Publication of International Patent Application No. 2012-518100 (US Publication No. 2010/205926).

FIG. 17 is a partial enlarged plan view of a nozzle plate employed in each of Japanese Patent Laid-open Publication No. 2009-91680 and National Publication of International Patent Application No. 2012-518100 (US Publication No. 2010/205926).

The nozzle plate in FIG. 17 has composite polymer discharge holes 15, and is provided with a sea polymer admission channel 11 (which has no discharge hole) in which pipes 20 are not arranged. Thus, even when the number of discharge holes increases, distribution of the sea polymer is kept satisfactory so that the sea polymer can be evenly supplied to the whole of a composite polymer discharge hole group. Therefore, even at the central part of the composite polymer discharge hole group, the sea polymer exists between island polymers so that merging of island polymers can be suppressed. Accordingly, in the spinneret technique in Japanese Patent Laid-open Publication No. 2009-91680 or National Publication of International Patent Application No. 2012-518100 (US Publication No. 2010/205926), a sea-island multicomponent fiber having a relatively large number of islands can be obtained even in a pipe type spinneret.

On the other hand, the distribution type spinneret is an effective technique in view of increasing the number of islands. A typical example thereof is a technique disclosed in Japanese Patent Laid-open Publication No. 2011-208313. FIG. 16 is a partial enlarged plan view of a nozzle plate having a shape disclosed in Japanese Patent Laid-open Publication No. 2011-208313.

In FIG. 16, discharge holes are arranged such that at least some of sea discharge holes 12 exist in a region surrounded by two common circumscribing lines 30 of an island discharge hole 13 provided in the nozzle plate and an island discharge hole 13 a neighboring the island discharge hole 13 with the shortest center-to-center distance, the island discharge hole 13 being considered as a reference. Therefore, in the nozzle plate in FIG. 16, the sea polymer is forcibly arranged between island polymers so that merging of island polymers discharged from the island discharge hole 13 and the island discharge hole 13 a can be suppressed. Accordingly, even when the distance between neighboring island discharge holes 13 is reduced to a working limit level, merging of island polymers can be prevented so that the number of discharge holes, through which the island polymer is discharged, can be made larger per cross-section area of the introducting hole.

As described above, even in conventional spinneret techniques, sea-island multicomponent fibers having a large number of islands can be produced by making various modifications. Currently, by dividing the island polymer into multiple segments according to the number of islands, even nanofibers having a fiber diameter in a nanometer order can be obtained, as described above. However, when the hole packing density is simply increased in the techniques described in Japanese Patent Laid-open Publication No. 2001-192924, Japanese Patent Laid-open Publication No. 2009-91680, National Publication of International Patent Application No. 2012-518100 (US Publication No. 2010/205926), and Japanese Patent Laid-open Publication No. 2011-208313, the distance between island components existing on the cross section of the sea-island multicomponent fiber decreases. Therefore, in a step of removing with a solvent a sea polymer for production of ultrafine fibers, the sea polymer dissolved in the solvent is not efficiently discharged from between island polymers or ultrafine fibers, and thus the efficiency of sea removal may be reduced. Accordingly, there is the problem that the time for the sea polymer to be completely removed increases, and particularly when nanofibers or the like are to be obtained, functions expected of nanofibers cannot be obtained due to degradation of nanofibers, aggregation of nanofibers, and so on.

As described above, a method of producing a sea-island multicomponent fiber by a composite spinneret in which the hole packing density of an island discharge hole is increased has been highly desired. However, failure to remove the sea polymer occurs during a sea removal treatment as described above, and this remains as a problem to be alleviated, causing an obstruction to production of ultrafine fibers. Therefore, solving this problem is of importance from an industrial point of view. Accordingly, it could be helpful to provide a sea-island multicomponent fiber with a sea component that can be soluble with high efficiency, and to provide a composite spinneret suitable for production of the sea-island multicomponent fiber.

SUMMARY

We thus provide:

(1) A multicomponent fiber including a sea component and an island component, wherein

in cross-section observation of the multicomponent fiber, the multicomponent fiber includes:

a sea-island region with the plurality of island components arranged in the sea component; and

one or more sea component regions formed only of the sea component between the sea-island region, and

the width (H) of the sea component region is larger than the maximum value of the distance (W) between island components existing in the sea-island region and neighboring each other.

(2) The multicomponent fiber according to (1), wherein the sea component region extends inward from a surface layer of the multicomponent fiber.

(3) The multicomponent fiber according to (1) or (2), wherein the island components in the sea-island region are regularly arranged.

(4) The multicomponent fiber according to any one of (1) to (3), wherein in cross-section observation of the sea-island multicomponent fiber, the ratio (L/D) of the length (L) of the sea component region to the diameter (D) of the multicomponent fiber is 0.25 or more.

(5) The multicomponent fiber according to any one of (1) to (4), wherein in cross-section observation of the sea-island multicomponent fiber, the width (H) of the sea component region is larger than the maximum diameter (d) of the island component.

(6) The multicomponent fiber according to (5), wherein in cross-section observation, there exists at least one sea component region where the width (H) of the sea component region is larger than the maximum diameter (d) of the island component, and the length (L1) of the sea component region is equal to or larger than ¼ of the diameter (D) of the multicomponent fiber.

(7) The multicomponent fiber according to any one of (1) to (6), wherein in cross-section observation, the width (H) of the sea component region and the diameter (D) of the multicomponent fiber satisfy the following formula:

0.001<H/D<0.2.

(8) The multicomponent fiber according to any one of (1) to (7), wherein in cross-section observation, the cross-section area (Ac) of the multicomponent fiber and the sum of areas (As) of sea component regions satisfy the following formula:

0.05≦As/Ac≦0.35.

(9) The multicomponent fiber according to any one of (1) to (8), wherein in cross-section observation, the sea region is cruciform.

(10) A method of producing an ultrafine fiber, including the step of: removing a sea component from the multicomponent fiber according to any one of (1) to (9).

(11) A fiber product including the fiber according to any one of (1) to (9).

(12) A fiber product including an ultrafine fiber obtained by the method according to (10).

(13) A composite spinneret for discharging a composite polymer composed of an island polymer and a sea polymer, the composite spinneret satisfying the requirements <1> and <2>:

<1> the composite spinneret includes:

a distribution device for distributing polymers;

a nozzle plate which is situated on the downstream side of the distribution device in a polymer spinning passage direction and which has a plurality of sea discharge holes, and at least one kind of discharge holes selected from a plurality of island discharge holes and a plurality of composite polymer discharge holes; and

a flow contraction plate which is situated on the downstream side of the nozzle plate in the polymer spinning passage direction and which has a introducting hole communicating with discharge holes in a combination of discharge holes that is selected from the combinations of:

-   -   the sea discharge holes and the island discharge holes;     -   the sea discharge holes and the composite polymer discharge         holes; and     -   the sea discharge holes, the island discharge holes and the         composite polymer discharge holes; and

<2> the nozzle plate has a nozzle hole collection including a plurality of discharge holes, and the nozzle hole collection includes a sea component region forming hole group including the sea discharge holes, and at least one sea-island discharge hole group including any of (i) to (v):

-   -   (i) the sea discharge holes and the island discharge holes;     -   (ii) the composite polymer discharge holes;     -   (iii) the sea discharge holes and the composite polymer         discharge holes;     -   (iv) the island discharge holes and the composite polymer         discharge holes; and     -   (v) the sea discharge holes, the island discharge holes and the         composite polymer discharge holes.

(14) The composite spinneret according to (13), wherein the composite spinneret further satisfies the requirement <3>:

<3> the sea component region forming hole group is continuously arranged inward from an outer periphery of the nozzle hole collection with a part of the sea-island discharge hole group held between both sides.

(15) The composite spinneret according to (13) or (14), wherein the distribution device has a plurality of composite polymer discharge holes, and is formed by stacking one or more distribution plates provided with a distribution hole and/or a distribution groove, and the distribution hole or the distribution groove communicates with at least one kind of discharge hole selected from the sea discharge hole, the island discharge hole and the composite polymer discharge hole.

(16) The composite spinneret according to any one of (13) to (15), wherein the distribution device has a plurality of composite polymer discharge holes, and includes:

a plurality of pipes for supplying the island polymer to the polymer discharge hole, the pipes arranged at positions corresponding to the composite polymer discharge holes of the nozzle plate on a one-to-one basis;

a sea polymer introduction channel for supplying the sea polymer; and

a sea polymer distribution chamber provided to communicate with the sea polymer introduction channel and surround the plurality of pipes, and

the composite polymer discharge hole of the nozzle plate communicates with the pipe and the sea polymer distribution chamber.

(17) The composite spinneret according to any one of (13) to (16), wherein a sea discharge hole that forms a part of the nozzle hole collection is arranged at each apex of an n-gonal lattice, an island discharge hole that forms a part of the nozzle hole collection is arranged at the gravity center position of the n-gonal lattice, m or less of the island discharge holes are arranged on an imaginary circumference, the radius of which is a center-to-center distance between the sea discharge hole that forms the sea component region forming hole group and the sea discharge hole or the island discharge hole closest to the sea discharge hole of the sea component region forming hole group, and n and m satisfy any of the requirements (x) to (xii):

(x) n=6 and m=2 (xi) n=4 and m=3 (xii) n=3 and m=5

(18) The composite spinneret according to any one of (13) to (17), wherein the sea component region forming hole group is continuously arranged from the outer periphery of a circumscribed circle of the nozzle hole collection having a radius of R to the inside of a circle having a radius of 0.5R or less from the center with the sea component region forming hole group held between both sides of the sea-island discharge hole group.

(19) The composite spinneret according to any one of (13) to (18), wherein the composite spinneret is used for production of the multicomponent fiber according to any one of (1) to (9).

(20) A method of producing a multicomponent fiber, including the step of: putting an island polymer and a sea polymer in the composite spinneret of a spinning machine using the composite spinneret according to any one of (13) to (18), and discharging the island polymer and the sea polymer from the composite spinneret to perform spinning.

(21) The method of producing a multicomponent fiber according to (20), wherein a multicomponent fiber to be produced is the multicomponent fiber according to any one of (1) to (9).

The meanings of terms used herein are as follows.

The “distribution hole” means a hole formed by combination of a plurality of distribution plates, the hole serving to distribute a polymer in a polymer spinning passage direction.

The “distribution groove” means a groove formed by combination of a plurality of distribution plates, the groove serving to distribute a polymer in a direction perpendicular to a polymer spinning passage direction. The distribution groove may be a long and narrow hole, or may be formed by digging a long and narrow groove.

The “polymer sinning passage direction” means a main direction in which each polymer passes from a distribution device to a nozzle hole of a spinneret.

The “composite polymer discharge hole” means a discharge hole through which a composite polymer is discharged, the composite polymer having an island polymer and a sea polymer merged with each other in a sheath-core form, a side-by-side form, a layered form, a sea-island form or a circumferential form.

The “hole packing density” means a value determined by dividing the sum of the number of island discharge holes and the number of composite polymer discharge holes by the sum of cross-section areas of introducting holes. Only island discharge holes may exist, or only composite polymer discharge holes may exist. The “diameter” in fiber cross-section observation when a diagram, the diameter of which is to be defined, is not a circle, means the diameter of a circle having an area equal to the area of the diagram. It is to be noted that the “diameter” means the diameter of a circumscribed circle of a fiber cross section for a fiber from which a sea component has been removed to leave only an island polymer.

The “center” of a diagram in fiber cross-section observation means the gravity center position.

The “sea removal” means that a sea polymer of a multicomponent fiber is removed with a solvent.

According to our multicomponent fibers, even when the number of island components per cross-section area of the multicomponent fiber is large, a sea component can be easily removed with a solvent efficiently so that an extremely thin ultrafine fiber can be obtained. According to the composite spinneret, the multicomponent fiber can be easily produced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic longitudinal sectional view of a composite spinneret that is used in an example.

FIG. 2 is a schematic longitudinal sectional view of a composite spinneret that is used in the example, a spinning pack and a cooler, and a periphery thereof.

FIG. 3 is a partial enlarged plan view of a nozzle plate that is used in the example.

FIG. 4 is a plan view of a nozzle plate that is used in the example.

FIG. 5 is a partial enlarged plan view of a nozzle plate that is used in the example.

FIG. 6 is a partial enlarged longitudinal sectional view of a nozzle plate that is used in the example.

FIG. 7 is a partial enlarged plan view of a nozzle plate that is used in the example.

FIG. 8 is a partial enlarged plan view of a nozzle plate that is used in the example.

FIG. 9 is a partial enlarged plan view of a nozzle plate that is used in the example.

FIG. 10 is a schematic longitudinal sectional view of a composite spinneret that is used in the example.

FIG. 11 is a partial enlarged plan view of a nozzle plate that is used in the example.

FIG. 12 is a partial enlarged plan view of a nozzle plate that is used in the example.

FIG. 13 is a sectional view of a multicomponent fiber as one example.

FIG. 14 is a sectional view of a multicomponent fiber as one example.

FIG. 15 is a partial enlarged longitudinal sectional view of a composite spinneret in a conventional example.

FIG. 16 is a partial enlarged plan view of a nozzle plate in a conventional example.

FIG. 17 is a partial enlarged plan view of a nozzle plate in a conventional example.

FIG. 18 is a partial enlarged plan view of a nozzle plate that is used in another example.

FIG. 19 is a partial enlarged plan view of a cross section of a multicomponent fiber.

FIG. 20 is a sectional view of a multicomponent fiber as one example.

FIG. 21 is a sectional view of a multicomponent fiber as one example.

FIG. 22 is a sectional view of a multicomponent fiber as one example.

FIG. 23 is a sectional view of a multicomponent fiber as one example.

FIG. 24 is a sectional view of a multicomponent fiber as one example.

FIG. 25 is a sectional view of a multicomponent fiber as one example.

FIG. 26 is a sectional view of a multicomponent fiber as one example.

FIG. 27 is a sectional view of one example of a conventional multicomponent fiber.

FIG. 28 is a partial enlarged plan view of a nozzle plate that is used in the example.

FIG. 29 is a partial enlarged plan view of a nozzle plate that is used in the example.

FIG. 30 is a partial enlarged plan view of a nozzle plate that is used in the example.

FIG. 31 is a partial enlarged plan view of a nozzle plate that is used in the example.

FIG. 32 is a partial enlarged plan view of a nozzle plate that is used in the example.

FIG. 33 is a partial enlarged plan view of a nozzle plate that is used in the example.

FIG. 34 is a partial enlarged plan view of a nozzle plate that is used in the example.

FIG. 35 is a partial enlarged plan view of a nozzle plate that is used in the example.

FIG. 36 is a partial enlarged plan view of a nozzle plate that is used in the example.

DESCRIPTION OF REFERENCE SIGNS

-   -   1: Distribution device     -   2: Nozzle plate     -   3: Flow contraction plate     -   4: Introducting hole     -   5: Flow contraction hole     -   6: Spinneret discharge hole     -   7: Composite spinneret     -   8: Spinning pack     -   9: Cooler     -   10: Spin block     -   11: Nozzle plate     -   12: Sea discharge hole     -   13: Island discharge hole     -   15: Composite polymer discharge hole     -   16: Measuring plate     -   17: Distribution plate     -   18: Nozzle hole collection     -   19: Sea-island discharge hole group     -   20: Pipe     -   21: Sea polymer introduction channel     -   22: Island polymer introduction channel     -   23: Sea polymer distribution chamber     -   30: common circumscribing line     -   40: Multicomponent fiber     -   41: Sea component     -   42: Sea-island region     -   43: Island component     -   44: Sea component region     -   51: Distribution groove     -   52: Distribution hole     -   61: Sea polymer introduction channel     -   62: Pipe     -   63: Sea polymer distribution chamber     -   64: Distribution device     -   65: Sea discharge hole     -   66: Composite polymer discharge hole 66     -   67: Nozzle plate

DETAILED DESCRIPTION

Our spinnerets, fibers, and methods will be specifically described below along with desirable examples.

A multicomponent fiber includes a sea-island region 42 with an island component 43 arranged in a sea component 41, and a sea component region 44 formed only of the sea component 41 as illustrated in FIG. 13.

The sea component region 44 means a region formed only of a sea polymer as shown in FIG. 13, the sea component region having a width (H) larger than the maximum value of a distance between island components existing in the sea-island region and neighboring each other. In the multicomponent fiber, the sea component region is between the sea-island region of the multicomponent fiber, and in cross-section observation, there are one or more sea component regions.

As described above, one of the purposes of the multicomponent fiber is production of an ultrafine fiber, and this structure is intended to ensure that the efficiency of the sea removal treatment is not reduced even if the island packing density is increased. In the cross section of a conventional multicomponent fiber with a large number of island components arranged in a sea component, the treatment with a solvent naturally proceeds from the outer layer of the multicomponent fiber gradually. Even island components are affected by the solvent before the sea removal treatment reaches the inner part of the multicomponent fiber. Therefore, there has been the problem that the resulting ultrafine fiber has significantly poor quality, or sea removal is not completed.

Thus, we provided a sea component region composed only of a sea polymer in cross-section observation as in the multicomponent fiber. That is, in the multicomponent fiber, the sea polymer in the sea component region is removed before the solvent dissolves the sea polymer existing in the sea-island region at the time of removing the sea polymer of the multicomponent fiber. Therefore, the solvent reaches the center of the multicomponent fiber early so that the elution time of the sea polymer can be reduced.

The distance between neighboring island components (inter-island component distance: W) in the sea-island region and the width (H) of the sea component region can be determined in the following manner.

The multicomponent fiber is embedded in an embedding medium such as an epoxy resin, and cut along the cross section by a microtome, and the cut surface is then photographed by a scanning electron microscope (SEM) at a magnification that allows the entire cross section to be observed. When the cross section is stained with a metal compound, a contrast difference between the island component and the sea component can be made clear. From cross-section images of 10 or more randomly selected multicomponent fibers, the width of the sea component region can be measured using image processing software. The inter-island component distance and width of the sea component region herein mean a distance between island components and width of the sea component region as expressed on an image of a cut surface where the cut surface is a cross section in a vertical direction with respect to the fiber axis from the image. The inter-island component distance refers to the minimum value between an island component and another island component for two island components neighboring each other in the sea-island region. The width of the sea component is calculated in the following manner. A boundary line between the sea component region and the sea-island component region is assumed. Points that form the boundary line are assumed, and the shortest distance between each point and a boundary line between the sea-island component and the sea-island region in the opposite direction is determined.

The inter-island component distance and the width of the sea component region are each measured in a unit of μm to the second decimal place, and rounded off to the first decimal place. The above procedure is carried out for each of 10 or more randomly extracted spots. For the island component distance, an average of the measured values is employed.

In cross-section observation as described above, when the sea component region exists with a large width, cracks are formed from the side surface to the central part of the multicomponent fiber in the early stage of the sea removal treatment so that a solvent easily infiltrates into the inner part of the multicomponent fiber. The formed cracks significantly propagate to the inner part of the multicomponent fiber so that the multicomponent fiber can be divided. Division of the multicomponent fiber into a plurality of fibers as described above is preferred because the specific surface area of the multicomponent fiber exposed to the solvent at the time of performing the sea removal treatment increases, leading to an increase in elution speed of the sea polymer. The specific surface area herein means the surface area per fiber mass.

As a criterion for development of such a phenomenon, the width (H) of the sea component region and the diameter (D) of the multicomponent fiber preferably satisfy the relationship of 0.001<H/D<0.2. When the above-mentioned relationship is satisfied, the multicomponent fiber is physically stimulated by a liquid flow during the sea removal treatment when the treatment is performed in a flow liquid in a jet dyeing machine or the like so that cracks that are once formed are expanded as the sea removal treatment proceeds. Further, a force is applied to the multicomponent fiber in the compression direction due to the effect of the liquid flow, and the multicomponent fiber is physically divided. In view of infiltration of a solvent into the inner part of the multicomponent fiber and ease of crack formation, H/D is preferably as large as possible, and H/D is preferably 0.01 or more, further preferably 0.03 or more. On the other hand, H/D is preferably 0.2 or less from the viewpoint of homogeneity of cross-section forms (e.g. diameter and shape) of the multicomponent fiber and a plurality of existing island components and ease of quality control by cross-section observation or the like.

To disseminate formation of cracks throughout the multicomponent fiber, it is desirable that the cross-section area (As) of the sea component region be in a certain ratio to the cross-section area (Ac) of the multicomponent fiber, and the relationship of 0.05≦As/Ac is preferably satisfied. Further, the relationship of As/Ac≦0.35 is preferably satisfied. Sea removal efficiency is improved as the parameter of As/Ac becomes larger. However, when the above-mentioned relationship is satisfied, the amount of the sea polymer used to form the sea component region is small, and also the sea polymer in an amount sufficient to form a sea-island cross section can be supplied to the sea-island region so that the sea-island multicomponent fiber can be produced with a high island component ratio. In addition to the homogeneity of island components and ease of quality control, the necessity to unduly increase the difficulty degree of design of a spinneret is eliminated.

The sea-island region existing in the multicomponent fiber refers to a region with a plurality of island components existing in a sea component as described above, and it is preferred that island components are regularly arranged in the sea-island region.

Preferably, the regular arrangement herein means that in four island components close to one another, straight lines connecting the centers of two neighboring island components (45-(a) (straight line connecting the centers of two island components) and 45-(b) (straight line connecting the centers of other two island components) in FIG. 19) are in parallel relationship with each other as illustrated in FIG. 19. The parallel relationship herein means that the angle formed by the two straight lines is not less than 0° and not more than 5°. In evaluation for the parallel relationship of island components, similarly to the case of the width of the sea component region, the following determination is made. That is, as described above, angles formed by two straight lines are measured to the first decimal place at 20 randomly selected spots in cross-section images of the multicomponent fiber, and when the value determined by rounding off the average of the measured values to an integer is in the above-mentioned range, it is determined that the island components are in parallel relationship with each other.

When island components are regularly arranged in the sea-island region in the multicomponent fiber, there is developed an effect of sustaining tension, which is applied to the multicomponent fiber in spinning and post processing, equally by the whole cross section of the multicomponent fiber so that spinning stability and post processability are significantly improved. In the sea-island multicomponent fibers, it is generally difficult to perform spinning at a high spinning velocity, but in the sea-island multicomponent fiber, spinning can be performed even at a high spinning velocity because island components are regularly arranged. Stress is not concentrated on a part of the fiber cross section and, therefore, the multicomponent fiber has excellent quality.

To enhance the effect of improving soluble efficiency of the sea component, the ratio (L/D) of the length (L) of the sea component region to the diameter (D) of the multicomponent fiber in the multicomponent fiber is preferably 0.25 or more (see, for example, FIG. 13). When the ratio (L/D) is in the above-mentioned range, cracks are generated in the sea component region in the early stage of the sea removal treatment, and a solvent infiltrates into the cracks to increase the specific surface area of the sea polymer exposed to the solvent so that the sea component can be efficiently removed. This is because the sea component is progressively removed by a treatment with a solvent. This effect results in embrittlement of the sea polymer, and since the sea component region is formed of the sea polymer which is easily dissolved, the sea component region is removed in the early stage of the elution treatment, and when the sea removal treatment is performed in a jet dyeing machine or the like, the sea component region is physically stimulated by a liquid flow so that cracks are easily formed.

Such crack formation due to embrittlement of the sea component region occurs when the ratio of the diameter of the composite cross section to the width of the sea component region is 0.25 or more, but L/D is preferably 0.50 or more. When the ratio (L/D) is in the above-mentioned range, cracks are formed over ½ or more of the multicomponent fiber diameter in the early stage of the elution treatment, and transversely propagate across the cross section of the multicomponent fiber as the sea removal treatment proceeds and further the fiber is physically stimulated, and ultimately the multicomponent fiber is divided into two halves. In this case, the specific surface area treated with the solvent increases in proportion to the square of the division number of the multicomponent fiber. Therefore, the sea removal efficiency is further improved. From this point of view, the length (L) of the sea component region is preferably as large as possible, the maximum viable value of the above-mentioned ratio is 1, and this value may be particularly preferred.

The width (H) of the sea component region is preferably larger than the maximum diameter (d) of the island component. This is because the effect of improving sea removal efficiency by arranging the sea component region essentially depends on the width (H) of the sea component region, but a width being larger than the maximum diameter (d) of the island component is preferred because infiltration of the solvent and crack formation properly proceed without being hindered by influences of island components.

Further, it is preferable that there exists at least one sea component region where the width (H) of the sea component region is larger than the maximum diameter (d) of the island component, and the length (L1) of the sea component region is equal to or larger than ¼ of the diameter (D) of the multicomponent fiber.

The method of evaluating the island component diameter is as follows. The cross section of the sea-island multicomponent fiber is photographed similarly to the case of the width of the sea component region, and an image is photographed at a magnification that allows 150 or more island components to be observed in multifilaments of the multicomponent fiber. Diameters of 150 island components randomly extracted from the photographed image are measured. The island component diameter herein means a diameter of an imaginary circle circumscribed to a cut surface at three or more points where the cut surface is a cross section in a vertical direction with respect the fiber axis from the image that is two-dimensionally photographed. The value of the island component diameter is measured to the first decimal place in a unit of nm, and rounded off to an integer. The diameters of the 150 photographed island components are measured, and the maximum value thereof is defined as the maximum diameter (d) of the island component.

The maximum diameter (d) of the island component is preferably smaller than the width (H) of the sea component region, and from the viewpoint of suppressing hindrance to crack formation as described above, H/d is more preferably 2.0 or more. The island component diameter is preferably 100 to 5000 nm. When the island component diameter is in this range, an effect of improving sea removal efficiency is obtained and, further, the ultrafine fiber subjected to the sea removal treatment has high quality and excellent characteristics. When the fiber diameter is 100 to 5000 nm, the effect of the sea component region becomes more remarkable without hindering the sea removal treatment, and also ultrafine fibers having extreme thinness unable to be achieved by a single spinning technique can be obtained.

Ultrafine fibers generated from the multicomponent fiber, when having a diameter of 5 μm or less, have soft touch and fineness that cannot be achieved with common fibers (several tens μm). By taking advantage of these characteristics, the ultrafine fibers can be used, for example, as a material for artificial leathers and high-texture apparels. In addition, by taking advantage of reduced fiber gaps, the ultrafine fibers can be formed into a high-density fabric, and used for sports wear required to have windbreaking performance and water repellency. Extremely thinned fibers enter fine grooves, and the specific surface area increases and contaminants are caught in fine voids between fibers. Therefore, high absorptivity and dust collecting performance are exhibited. By taking advantage of these characteristics, the ultrafine fibers can be used for wiping cloths and precise polishing cloths for precision equipment in applications of industrial materials. Since a high level of wiping performance and the like is required particularly when the ultrafine fibers are to be used for polishing and wiping for IT, the diameter of the ultrafine fiber is preferably as small as possible. A range of 100 to 1000 nm may be a more preferred range. The island component diameter thereof may be less than 100 nm, but the island component diameter is preferably 100 nm or more from the viewpoint of handling characteristics during the sea removal treatment.

The multicomponent fiber is suitably used for production of the above-mentioned ultrafine fibers and fiber products composed of the ultrafine fibers. Therefore, improvement of basic characteristics of ultrafine fibers such as mechanical properties, which has been difficult heretofore, can be achieved, and by improving homogeneity of the resulting ultrafine fiber bundles, fiber products composed thereof can be improved in quality.

In multicomponent fibers intended to generate ultrafine fibers, generally the island polymer is a hardly soluble component and the sea polymer is an easily soluble component. For example, the island polymer may be a polyethylene terephthalate (PET), and the sea polymer may be a copolymerized PET to form an easily soluble component. In this case, the copolymerized PET as the sea polymer has a higher solubility with a solvent as compared to the island polymer. However, when efficiency of the sea removal treatment is poor so that it takes a long time for the sea polymer to be completely removed, even the island polymer may be treated with a solvent. Particularly when the island component diameter is small, this effect is very significant. Particularly when the island component diameter is in the order of μm, the specific surface area thereof increases so that the quality may be degraded, for example, mechanical properties of ultrafine fiber bundles are deteriorated, or the island component arranged on the outermost layer and the island component arranged on the inner layer in the multicomponent fiber have different diameters.

The sea component region is arranged, and thus the inner part of the multicomponent fiber is affected by the treatment with a solvent in the early stage of the sea removal treatment so that degradation in quality which has been the problem with conventional multicomponent fibers is extremely small. Even if the island packing density is increased, ultrafine fibers composed of the island polymer can be produced with a high yield with respect to multicomponent fibers as a raw material by increasing the ratio of the island polymer to the sea polymer. Further, by increasing the island polymer ratio, stress in a process for producing fiber (spinning and drawing) can be efficiently propagated to island components, and therefore the fiber structure of the island component can be highly generated. Therefore, mechanical properties of ultrafine fibers can be improved, and also orientation crystallization of the island component proceeds so that its resistance to a solvent can be improved.

As described above, owing to existence of the sea component region as a requirement, reduction in sea removal efficiency, which has raised a problem heretofore, can be avoided even if the island packing density is increased. Therefore, fibers can be extremely thinned by increasing the number of islands and, further, by increasing the ratio of the island component, ultrafine fibers having excellent basic characteristics such as mechanical properties can be stably produced with high productivity. The sea component region having the above-mentioned effect exhibits the effects including those illustrated in FIGS. 13, 14 and 20 to 26 when our range is satisfied. Particularly, it is effective that the sea component region is arranged inward from the surface of the multicomponent fiber. When the sea component region exists with a certain degree of cross-section area ratio, division of the multicomponent fiber due to crack formation efficiently proceeds. Further, to advance the concept of division of the multicomponent fiber due to crack formation, it is preferred that the sea-island component region is widely arranged on the cross section of the multicomponent fiber. Particularly, it is preferred that the sea component region is cruciformly arranged as shown in FIG. 13.

The sea-island multicomponent fiber preferably has a strength at break of 0.5 to 10.0 cN/dtex and an elongation of 5 to 700%. The strength herein is a value obtained by determining a load-extension curve of multifilaments under conditions as shown in JIS L 1013 (1999), and dividing the load value at rupture by the initial fineness, and the elongation is a value obtained by dividing the extension at rupture by the initial test length. The initial fineness means a value obtained by calculating the mass per 10000 m from the simple average of a plurality of measurements of the mass of the fiber per unit length. The strength at break of the sea-island multicomponent fiber is preferably 0.5 cN/dtex or more in view of passage through the post processing step and endurability of the fiber in actual use. The upper limit of the strength at break of fibers that can be produced is about 10.0 cN/dtex. The elongation is preferably 5% or more in view of passage through the post processing step. An upper limit value of the elongation of fibers that can be produced is generally 700%. The strength at break and elongation can be adjusted by controlling conditions in the production process according to the intended application.

When ultrafine fibers obtained from the sea-island multicomponent fiber are used in applications of general clothes such as inner and outer clothes, it is preferred that the strength at break is 1.0 to 4.0 cN/dtex and the elongation is 20 to 40%. In applications of sports wear and the like in which use conditions are relatively severe, it is preferred that the strength at break is 3.0 to 5.0 cN/dtex and the elongation is 10 to 40%. In applications other than those of clothes, the ultrafine fibers may be used for wiping cloths and polishing cloths. In these applications, a fiber product is rubbed against an object while being pulled under weight. Thus, it is preferred that the strength at break is 1.0 cN/dtex or more and the elongation is 10% or more. By setting the mechanical properties in the above-mentioned range, for example, the ultrafine fiber is prevented from being cut to come off during wiping or the like.

The sea-island multicomponent fiber can be formed into a variety of intermediates such as fiber winding packages and tows, cut fibers, cotton, fiber balls, cords, piles, fabrics and nonwoven fabrics, and subjected to a sea polymer elution treatment to generate ultrafine fibers, from which various fiber products are obtained. The sea-island multicomponent fiber can be used in an untreated state, partially freed of a sea polymer, or subjected to a treatment for removal of an island polymer to obtain a fiber product.

The fiber products may be used in applications of livingware such as common clothes such as jackets, skirts, pants and underclothes, sports wear, clothing materials, interior products such as carpets, sofas and curtains, vehicle interiors such as car seats, cosmetics, cosmetic masks, wiping cloths and health equipment; applications of environmental/industrial materials such as polishing cloths, filters, harmful substance removal products and separators for batteries; and applications of medical products such as sutures, scaffolds, artificial blood vessels and blood filters.

A method of producing the multicomponent fiber and a composite spinneret that can be used in production of the multicomponent fiber will be described in detail below with reference to the drawings.

FIG. 1 is a schematic sectional view of a composite spinneret as one example. FIG. 2 is a schematic sectional view of a composite spinneret 7, a spinning pack 8 that is used along with the composite spinneret 7, a cooler 9, and a periphery thereof. FIG. 4 is a plan view of a nozzle plate that is used as one of our examples, and FIG. 5 is a partial enlarged plan view of FIG. 4. FIGS. 3, 7, 8, 9, 11, 12, 18 and 27 to 35 are partial enlarged plan views of nozzle plates that are used in various examples. They are schematic views and depictions in the drawings are simplified. In the composite spinneret, the number of holes and grooves, their dimension ratios and so on are not limited to those shown in the drawings, and can be changed in accordance with the examples.

The composite spinneret 7 used in the example is mounted in the spinning pack 8, and fixed in a spin block 10 as shown in FIG. 2. The cooler 9 is provided below the composite spinneret 7. The composite spinneret 7 is formed by stacking a distribution device 1 for distributing polymers, a nozzle plate 2 and a flow contraction plate 3 in order as shown in FIG. 1. As shown in FIG. 5, the nozzle plate 2 is provided with island discharge holes 13 for discharging an island polymer, or sea discharge holes 12 for discharging a sea polymer, and sea-island discharge hole groups with the island discharge holes 13 and the sea discharge holes 12 forming a group, and sea component region forming hole groups with only the sea discharge holes 12 forming a group form a nozzle hole collection 18.

A polymer of each component distributed by a distribution device (not illustrated) is discharged from the island discharge holes 13 or the sea discharge holes 12 shown in FIG. 5, and a polymer of each component merges with each other to form a composite polymer flow. Thereafter, the composite polymer flow passes through introducting holes 4 and flow contraction holes 5 of the flow contraction plate shown in FIG. 1, and is discharged from spinneret discharge holes 6. The composite polymer flow is discharged from the spinneret discharge holes 6 shown in FIG. 2, and then cooled and solidified by an air flow jetted from the cooler 9. Thereafter, an oil is supplied to the composite polymer flow, and then the composite polymer flow is wound as a sea-island multicomponent fiber. In FIG. 2, a circular cooler 9 that jets an air flow circularly and inward, but a cooler that jets an air flow in one direction may be used.

Means for making it possible to reduce the sea removal time by improving sea removal efficiency during sea removal treatment will now be described.

As illustrated in FIG. 5, the nozzle plate used in the composite spinneret in the example has a sea component region forming hole group including a plurality of sea discharge holes 12, and at least one discharge hole group for forming a sea-island region (hereinafter, referred to as a “sea-island discharge hole group”), the discharge hole group including any of the following (i) to (v), and these discharge holes are combined to form one nozzle hole collection. The sea component region forming hole group is continuously arranged with being between the sea-island discharge hole group. An arrangement of the sea-island discharge hole group including the combination (i) is illustrated in FIG. 5, an arrangement of the sea-island discharge hole group including the discharge holes (ii) is illustrated in FIG. 3, an arrangement of the sea-island discharge hole group including the combination (iii) is illustrated in FIG. 9, an arrangement of the sea-island discharge hole group including the combination (iv) is illustrated in FIG. 11, and an arrangement of the sea-island discharge hole group including the combination (v) is illustrated in FIG. 18.

(i) the sea discharge holes 12 and the island discharge holes 13

(ii) the composite polymer discharge holes 15

(iii) the sea discharge holes 12 and the composite polymer discharge holes 15

(iv) the island discharge holes 13 and the composite polymer discharge holes 15

(v) the sea discharge holes 12, the island discharge holes 13 and the composite polymer discharge holes 15

Thus, the polymers discharged from the sea-island discharge hole group and the sea component region forming hole group of the nozzle plate merge with each other in the introducting hole, and are then discharged from the spinneret discharge hole to form a multicomponent fiber having a sea component region and a sea-island region.

As one example, a principle that a sea component region can be formed where the arrangement of the sea-island discharge hole group corresponds to (i) will be described in accordance with the flow of the polymer.

The island polymer and the sea polymer are simultaneously discharged to the downstream side from the nozzle plate 2 shown in FIG. 1. The discharged polymers flow along a polymer spinning passage direction, and are widened in a direction vertical to the polymer spinning passage direction so that neighboring polymers merge with each other to form a composite polymer flow. To produce a multicomponent fiber having the sea component region 44 as shown in FIG. 13, it is effective that the nozzle plate is provided with a sea-island discharge hole group including only the sea discharge holes 12 as shown in FIG. 5. However, the discharged polymer moves to be widened to fill a channel space and, therefore, it is difficult to form the sea component region 44 on the cross section of the multicomponent fiber merely by increasing the distance between sea-island discharge hole groups as shown in FIG. 17. In a nozzle plate as shown in FIG. 17, widening of the polymer is enlarged. Therefore, the cross section of the fiber is destabilized due to deviation of the arrangement of the island polymer and the like so that island components are not uniformly formed in the multicomponent fiber.

It is effective that the sea-island discharge hole group is arranged on the composite spinneret to be separated into four parts, and the sea discharge holes 12 are provided in the resulting gap as shown in FIG. 5. In the nozzle plate shown in FIG. 5, sea discharge holes 12 a for the sea component region exist in the gap formed by separation of the sea-island discharge hole group, and thus the widening of the sea-island region can be suppressed to inhibit destabilization of the fiber cross section.

In FIG. 5, two or less island discharge holes 13 are arranged on an imaginary circumference with the sea discharge hole 12 a as a center, the radius of which is a center-to-center distance between the sea discharge hole 12 a and a discharge hole closest to the sea discharge hole 12 a among the sea discharge holes 12 or the island discharge holes 13 close to the sea discharge hole 12 a so that a sea component region forming hole group including a plurality of sea discharge holes 12 a is formed. The sea component region forming hole group is continuously arranged with a part of the sea-island discharge hole group held between both sides as shown in FIG. 5 so that a multicomponent fiber having the sea component region 44 as shown in FIG. 3 is obtained. In the nozzle plate shown in FIG. 5, the sea discharge hole 12 is arranged at each apex of a hexagonal lattice as an arrangement pattern of holes in the sea-island discharge hole group, and the island discharge hole 13 is arranged at the gravity center position of the hexagon that forms the lattice. The hole arrangement shown in FIG. 5 satisfies n=6 and m=2, with the sea discharge holes 12 surrounding the periphery of the island discharge hole 13. Therefore, even when the island polymer ratio increases, the sea polymer necessarily exists between island polymers so that merging of polymers from neighboring island discharge holes can be suppressed.

As other arrangement patterns of the sea-island discharge hole group, a tetragonal lattice is shown in FIG. 7, and a trigonal lattice is shown in FIG. 8.

The arrangement shown in FIG. 7 satisfies n=4 and m=3. In this case, as compared to the hexagonal lattice shown in FIG. 5, the distance between neighboring island discharge holes can be reduced and, therefore, the hole packing density can be further increased. The arrangement shown in FIG. 8 satisfies n=3 and m=5. In this case, as compared to the tetragonal lattice shown in FIG. 7, neighboring island discharge holes 13 can be made closer to each other. Therefore, the hole packing density can be further increased. Thus, in terms of an arrangement pattern of the sea-island discharge hole group, the hole packing density can be increased in the order of a trigonal lattice, a tetragonal lattice and a hexagonal lattice. However, spinning conditions such as the island polymer ratio may be restricted and, therefore, it is preferred to determine the arrangement pattern of holes in accordance with the cross-section form of an intended multicomponent fiber.

Next, the distribution device will be described with reference to FIG. 6. FIG. 6 is a partial enlarged longitudinal sectional view of a nozzle plate. The distribution device is formed by stacking one or more thick plates called measuring plate(s) 16 and one or more thin plates called distribution plate(s) 17. The measuring plate 16 and the distribution plate 17 are placed by a positioning pin to align with the center position (core) of the composite spinneret 7. The measuring plate 16 and the distribution plate 17 can also be fixed by a screw or a bolt. Also, it is preferred that the plates are metal-bonded (diffusion-bonded) by thermocompression bonding or the like for suppressing leakage of a polymer from a gap between members.

The measuring plate 16 in FIG. 6 is processed to have a channel groove and a channel hole for distributing the island polymer and the sea polymer and supplying the polymers to the distribution plate 17. The channel hole applies a constant channel pressure loss to the polymer so that the polymer can be uniformly supplied to an inflow channel of the distribution plate 17 positioned on the top part.

The distribution plate 17 is provided with a distribution groove 51 and/or a distribution hole 52 to distribute the island polymer and the sea polymer. The distribution groove 51 serves to guide the polymer in a direction vertical to the polymer spinning passage direction (leftward arrows and rightward arrows in FIG. 6), and the distribution hole 52 serves to guide the polymer in the polymer spinning passage direction (downward arrows in FIG. 6). When the distribution plate 17 having the distribution hole 52 and the distribution plate 17 having the distribution groove 51 are alternately stacked, one distribution groove 51 communicating with one distribution hole 52 at a position on the downstream side in the polymer spinning passage direction is formed. Therefore, a tournament type channel that forms a plurality of distribution holes 52 each communicating with the end of the distribution groove 51 is formed so that the polymer of each component distributed by the measuring plate 16 can be evenly divided into smaller quantity polymers.

Then, as another example, the arrangement corresponding to (ii) will be described with reference to FIG. 3 that is a partial enlarged plan view of the nozzle plate and FIG. 10 that is a schematic longitudinal sectional view of the composite spinneret. The nozzle plate shown in FIG. 3 shows that the sea-island discharge hole group includes composite polymer discharge holes. The nozzle plate shown in FIG. 3 is generally called a pipe type spinneret, with the sea-island discharge hole group including composite polymer discharge holes 15. As shown in FIG. 10, a distribution device 64 is provided with pipes 62 to supply the island polymer, sea polymer introduction channels 61 to supply the sea polymer, and a sea polymer distribution chamber 63 communicating with the sea polymer introduction channels 61. The pipes 62 of the distribution device 64 are formed to communicate with composite polymer discharge holes 66 of the sea-island discharge hole group on a one-to-one basis. The sea polymer distribution chamber 63 is formed to communicate with composite polymer discharge holes 66 and a sea discharge hole 65 of the sea component region forming hole group. The island polymer discharged from the pipes 62 of the sea-island discharge hole group and the sea polymer discharged from the sea polymer distribution chamber 63 merge with each other in the composite polymer discharge hole 66. The resulting composite polymer flow has a sheath-core structure in which the island polymer forms a core and the sea polymer forms a sheath.

On the other hand, the sea polymer is supplied from the sea polymer distribution chamber 63 to the sea discharge hole 65 of the sea component region forming hole group. The composite polymer discharged from the sea-island discharge hole group and the sea polymer discharged from the sea component region forming hole group merge with each other on the lower surface of a nozzle plate 67. Since the sea polymer discharged from the sea component region forming hole group exists between composite polymer flows, a multicomponent fiber with a sea component region formed on our cross section can be produced.

Then, as another example, a case where the arrangement of a sea-island discharge hole group 19 corresponds to (iii) will be described with reference to FIG. 9. In the nozzle plate in FIG. 9, the sea-island discharge hole group includes composite polymer discharge holes 15 and sea discharge holes 12. Each polymer supplied from a distribution device (not illustrated) is distributed, and supplied to each hole of the nozzle plate. In the composite polymer discharge hole 15 of the sea-island discharge hole group shown in FIG. 9, the sea polymer and the island polymer merge with each other to form a composite polymer flow, and the composite polymer flow is discharged. In the sea discharge hole 12, only the sea polymer is discharged. The polymers are discharged from the composite polymer discharge holes 15 and the sea discharge holes 12 of the sea-island discharge hole group, and the polymers merge with each other to form a composite polymer flow having a sea-island form. The feature of the form shown in FIG. 9 is that the sea-island discharge hole group is provided with the sea discharge holes 12 in addition to the composite polymer discharge holes 15. Therefore, the sea polymer is arranged on the periphery of the composite polymer flow in a sheath-core form (core: island polymer and sheath: sea polymer), which is formed by the composite polymer discharge holes 15. Accordingly, in the multicomponent fiber shown in FIG. 13, the distance between the island components 43 can be increased. Therefore, a solvent easily infiltrates between the island components 43 in the sea removal treatment so that the sea removal time of the sea polymer can be reduced. In such a form, generally island polymers may merge with each other as the ratio of the island component is increased, but this form is preferred from the viewpoint of suppressing merging of island polymers because the sea polymer exists in a large amount between island polymers.

Then, as another example, a case where the arrangement of the sea-island discharge hole group 19 corresponds to (iv) will be described. FIG. 11 is a partial enlarged plan view of a nozzle plate. In the nozzle plate in FIG. 11, the sea-island discharge hole group includes composite polymer discharge holes 15 and island discharge holes 13. Each polymer supplied from a distribution device (not illustrated) is distributed, and supplied to each hole of the nozzle plate. In the composite polymer discharge hole 15 of the sea-island discharge hole group, the sea polymer and the island polymer merge with each other, and the resulting composite polymer flow is discharged. In the island discharge hole 13, only the island polymer is discharged. The feature of the form shown in FIG. 11 is that the island discharge hole group is provided with the island discharge holes 13 in addition to the composite polymer discharge holes 15. Therefore, a composite polymer flow with the island polymer existing on the periphery of a polymer flow in a sheath-core form (core: island polymer and sheath: sea polymer) can be formed. As a result, as compared to the arrangement (ii) shown in FIG. 3, the hole packing density can be increased so that a larger number of island components can be arranged on the cross section of the multicomponent fiber.

Then, as another example, a case where the arrangement of the sea-island discharge hole group corresponds to (v) will be described. FIG. 18 is a partial enlarged plan view of a nozzle plate. In the nozzle plate in FIG. 18, the sea-island discharge hole group includes composite polymer discharge holes 15, sea discharge holes 12 and island discharge holes 13. Each polymer supplied from a distribution device (not illustrated) is distributed, and supplied to each hole of the nozzle plate. In the composite polymer discharge hole 15 of the sea-island discharge hole group, the sea polymer and the island polymer merge with each other, and the resulting composite polymer flow is discharged. In the island discharge hole 13, only the island polymer is discharged, and in the sea discharge hole 12, only the sea polymer is discharged. The feature of the nozzle plate shown in FIG. 18 is that the island discharge hole group is provided with the island discharge holes 12 and the sea discharge holes 13 in addition to the composite polymer discharge holes 15. Therefore, a composite polymer flow with a sea polymer surrounding a sheath-core (core: island polymer and sheath: sea polymer) polymer and an island polymer can be formed. Accordingly, the number of island components in the multicomponent fiber is larger as compared to the arrangement (iv) shown in FIG. 11, and smaller as compared to the arrangement (iii) shown in FIG. 9. On the other hand, the distance between island components is larger as compared to the arrangement (iii) shown in FIG. 9, and smaller as compared to the arrangement (iv) shown in FIG. 11. Therefore, the effect of increasing the number of islands and improving the sea removal efficiency of the sea polymer is not lower as compared to the arrangement (iii) and not higher as compared to the arrangement (iv).

FIGS. 9, 11 and 18 in which a pipe type spinneret is used show an example in which a composite polymer flow formed by the composite polymer discharge holes 15 has a sheath-core structure of an island polymer and a sea polymer, but this disclosure is not limited to the example. The composite polymer flow may be a side-by-side form, a multi-layered form or a sea-island form, and can be formed diversely according to the state of distribution or merging of the polymers in the distribution device.

Also, when the sea component region forming hole group is continuously arranged from the outer circumference of a circumscribed circle of the nozzle hole collection 18 to a region with a radius of 0.5R or less where R is the radius of the circumscribed circle of the nozzle hole collection 18, with a part of the sea-island discharge hole group surrounding both sides of the sea component region forming hole group as shown in FIG. 12, good fibers can be achieved. A removing discharge hole group is not necessarily cruciformly arranged, and may be arranged in a radial form, a latticed form, or in the form of three parallel lines, and the important point here is that the sea component region forming hole group is arranged with a part of the sea-island discharge hole group being in contact with both sides.

Next, in common with the composite spinnerets and nozzle plates shown in FIGS. 1-8, 10 and 12, shapes and the like of the members will be described in detail.

The shape of the composite spinneret 7 shown in FIG. 1, when seen from above, is not limited to a circular shape, and may be a tetragonal shape or a polygonal shape. The arrangement of the spinneret discharge holes 6 in the composite spinneret 7 shown in FIG. 1 or the nozzle hole collection 18 shown in FIG. 4 may be changed in accordance with the number of sea-island multicomponent fibers, the number of yarn threads and a cooler. When the cooler 9 shown in FIG. 2 is a circular cooler, it is preferred to circularly arrange the spinneret discharge holes or the nozzle hole collection over one line or a plurality of lines. When the cooler 9 shown in FIG. 2 is a unidirectional cooler, it is preferred to arrange the spinneret discharge holes or the nozzle hole collection in zigzags.

Each channel hole to discharge the polymer of each component may have any shape such as a circular shape, a polygonal shape or a star shape. Depending on the example, each channel hole may be made variable such that, for example, the cross section is changed along the polymer spinning passage direction.

The introducting hole 4 shown in FIG. 1 is provided with a definite approach zone extending from the lower surface of the nozzle plate 2 in the polymer spinning passage direction, and thus serves to stabilize the composite polymer flow by reducing the flow rate difference immediately after the island polymer and the sea polymer merge with each other. It is preferred that the hole diameter of the introducting hole 4 is larger than the diameter of a circumscribed circle of the nozzle hole collection provided on the nozzle plate 2, and that the ratio of the cross-section area of the circumscribed circle of the nozzle hole collection to the cross-section area of the introducting hole 4 is as small as possible. When the introducting hole 4 is formed as described above, widening of each polymer discharged from the nozzle plate 2 is suppressed so that the composite polymer flow can be stabilized.

When the reduction angle α of a channel extending from the introducting hole 4 to the spinneret discharge hole 6 in the flow contraction hole 5 shown in FIG. 1 is set to fall in the range of 50 to 90°, the composite spinneret 7 can be downsized, and an instable phenomenon such as draw resonance of the composite polymer flow can be suppressed to stably supply the composite polymer flow.

Next, in common with the composite spinneret of the example, a method of producing a multicomponent fiber will be described in detail.

The method of producing a multicomponent fiber can be carried out using a known composite spinning machine, and it is preferred to use the composite spinneret 7 shown in FIG. 1 from the viewpoint of controlling our unique composite cross section.

We produce a sea-island multicomponent fiber to generate ultrafine fibers and, therefore, examples of the island polymer and sea polymer include melt-moldable polymers such as polyethylene terephthalate or copolymers thereof, polyethylene naphthalate, polybutylene terephthalate, polytrimethylene terephthalate, polypropylene, polyolefins, polycarbonate, polyacrylate, polyamide, polylactic acid and thermoplastic polyurethane. Particularly, polycondensation-based polymers represented by polyester and polyamide are preferred because they have a high melting point. The melting point of the polymer is preferably 165° C. or more in view of high heat resistance. The polymer may contain various kinds of additives such as an inorganic material such as titanium oxide, silica or barium oxide, a colorant such as carbon black, a dye or a pigment, a flame retardant, a fluorescent brightening agent, an antioxidant and an ultraviolet absorber. When considering a sea removal treatment or an island removal treatment, the polymer can be selected from melt-moldable polymers which are more easily soluble than other components, such as polyester and copolymers thereof, polylactic acid, polyamide, polystyrene and copolymers thereof, polyethylene and polyvinyl alcohol. The easily soluble component is preferably copolymerized polyester, polylactic acid, polyvinyl alcohol or the like which is easily soluble in an aqueous solvent or hot water, and in particular, polyester and polylactic acid copolymerized with polyethylene glycol and/or sodium sulfoisophthalic acid alone or in combination are preferable from the viewpoint of spinnability and solubility in low-concentration aqueous solvents. Polyester copolymerized with sodium sulfoisophthalic acid alone is particularly preferable from the viewpoint of the ease of sea removal and fiber openability of the resulting ultrafine fibers.

To identify an appropriate combination of a hardly soluble component and an easily soluble component as described above, it is practical to select an appropriate hardly soluble component suitable for the intended use and then select an appropriate easily soluble component that can be spun at the same spinning temperature, on the basis of the melting point of the hardly soluble component. When the molecular weight and the like of each component is adjusted with the above-mentioned melt viscosity ratio taken into consideration, homogeneity of island components of the sea-island multicomponent fiber in terms of fiber diameter and cross-sectional shape can be improved. When ultrafine fibers are to be generated from the sea-island multicomponent fiber, a difference in speed of dissolution between the hardly soluble component and the easily soluble component in a solvent used for sea removal is preferably large from the viewpoint of stability of the cross-sectional shape and retention of mechanical properties of ultrafine fibers, and a combination should be selected from the above-mentioned polymers based on a dissolution speed ratio ranging from 10 to 3000. From the viewpoint of their melting points, preferred combinations of polymers for obtaining ultrafine fibers from the sea-island multicomponent fiber include, for example, combinations of polyethylene terephthalate copolymerized with 1 to 10 mol % of 5-sodium sulfoisophthalic acid as a sea polymer and polyethylene terephthalate or polyethylene naphthalate as an island polymer; and combinations of polylactic acid as a sea polymer and nylon 6, polytrimethylene terephthalate or polybutylene terephthalate as an island polymer.

The spinning temperature in spinning of the sea-island multicomponent fiber is equal to or higher than a temperature at which one of two or more polymers that has the highest melting point or viscosity is flowable. The temperature at which the polymer is flowable, although it depends on the molecular weight, is indicated by the melting point of the polymer, and may be set at up to 60° C. above the melting point. Such a temperature is preferable because thermal decomposition of polymers in a spinning head or a spinning pack is prevented to suppress a decrease in molecular weight. The through-put rate of the polymer in the production method may be 0.1 g/min/hole to 20.0 g/min/hole per nozzle hole as a range that allows the polymer to be stably discharged. It is preferable that at this time the pressure loss in the nozzle hole, which can ensure discharge stability, is taken into consideration. It is preferred that, with the pressure loss herein considered to be 0.1 MPa to 40 MPa, the through-put rate is selected from the above-mentioned range in relation to the melt viscosity of the polymer, the nozzle hole diameter and the nozzle hole length. In the production method, the ratio of the island component (hardly soluble component) to the sea component (easily soluble component) can be selected from 10/90 to 95/5 in terms of the ratio of sea component/island component on the basis of the mass of each polymer through-put rate. It is preferred that the ratio of the island component is increased in the ratio of sea component/island component from the viewpoint of productivity of ultrafine fibers. The ratio of sea component/island component is more preferably 20/80 to 50/50 for producing multicomponent fibers and ultrafine fibers efficiently while maintaining stability by the production method from the viewpoint of long-term stability of the cross section of the sea-island multicomponent fiber. The sea-island composite polymer flow thus discharged from the composite spinneret is cooled and solidified, supplied with a spinning oil, and taken up by a roller, the circumferential speed of which is controlled, to form a sea-island multicomponent fiber. While the spinning velocity may be determined from the through-put rate and the intended fiber diameter, the spinning velocity is preferably 100 to 7000 m/min in the production method. The fiber can be made to have not only a circular shape, but also a shape other than a circular shape, such as a trigonal shape or a flat shape, or hollowed by changing the shape of the spinneret discharge hole 6. Further, the multicomponent fiber may have one yarn thread as a monofilament, or two or more yarn threads as a multifilament. The spun multicomponent fiber may be wound up and then drawn from the viewpoint of improving mechanical properties by enhancing orientation, or may be subsequently drawn without being wound up. As the drawing conditions, for example, in a drawing machine including at least one pair of rollers, a fiber composed of a thermoplastic polymer that is generally capable of being melt-spun is well drawn out in a fiber axis direction in response to the circumferential speed ratio of a first roller set at a temperature that is not lower than the glass transition temperature and not higher than the melting point to a second roller set at a temperature equivalent to the crystallization temperature, and the fiber is subjected to heat-setting and wound up so that the multicomponent fiber having a sea-island multicomponent fiber cross section as shown in FIG. 7 can be obtained.

In a polymer exhibiting no glass transition, the dynamic elasticity (tans) of the multicomponent fiber is measured, and a temperature equal to or higher than the peak temperature on the high-temperature side of the obtained tans may be selected as a preheating temperature. It is also preferred to perform the drawing step in multiple stages from the viewpoint of increasing the stretch ratio to improve mechanical properties.

To obtain ultrafine fibers from the thus obtained sea-island multicomponent fiber, the multicomponent fiber is immersed in a solvent or the like in which an easily soluble component can be removed so that the easily soluble component is removed, i.e. a sea removal step is performed, and thus ultrafine fibers composed of a hardly soluble component can be obtained. When the easily soluble component is copolymerized PET, polylactic acid (PLA) or the like copolymerized with 5-sodium sulfoisophthalic acid or the like, an aqueous alkali solution such as an aqueous sodium hydroxide solution can be used. As a method of treating the multicomponent fiber with an aqueous alkali solution, for example, the multicomponent fiber or a fiber structure formed thereof may be immersed in an aqueous alkali solution. Heating the aqueous alkali solution to 50° C. or more is preferable because hydrolysis can be accelerated. The use of a fluid dyeing machine or the like for the treatment is preferable from an industrial point of view because a large batch can be processed at a time to achieve high productivity. Thus, the method of producing the ultrafine fiber is described above on the basis of a common melt spinning technique, but needless to say, meltblowing and spunbonding can be used for its production, and further, a wet or a dry-wet solution spinning technique can also serve for its production.

EXAMPLES

The ultrafine fiber will be described in detail below by way of examples. For examples and comparative examples, evaluations were performed as described below.

A. Intrinsic Viscosity (IV)

The measurement was performed at 25° C. using ortho-chlorophenol as a solvent.

B. Melt Viscosity of Polymers

Chips of a polymer were dried in a vacuum dryer down to a moisture content of 200 ppm or less, and subjected to melt viscosity measurement in Capilograph 1B manufactured by Toyo Seiki Seisaku-sho, Ltd. in which the strain speed was changed in stages. The measuring temperature was set to about the spinning temperature, and the melt viscosity at 1,216 s⁻¹ was shown in examples and comparative examples. The measurement was started 5 minutes after feeding a sample into a heating furnace and performed in a nitrogen atmosphere.

C. Fineness

In a sea-island multicomponent fiber, the mass per 100 m was measured and multiplied by 100 to calculate the fineness. In an ultrafine fiber obtained by removing 99% or more of a sea component from the multicomponent fiber, the mass per 10 m was measured and multiplied by 1000 to calculate the fineness. Weighing of these samples was performed in an atmosphere at a temperature of 25° C. and a humidity of 55% RH.

The same procedure was repeated 10 times, and the simple average thereof was rounded off to the first decimal place in a unit of dtex to determine the fineness. Removal sea is evaluated based on the weight reduction rate of the sample on the premise that the sea removal rate of the sea polymer and the weight reduction rate of the sample (equation described below) are the same value.

Weight reduction rate (%)=(1−weight of sample after elution treatment/weight of sample before elution treatment)×100

D. Mechanical Properties of Fibers

A tensile tester “Tensilon” (registered trademark) Model UCT-100 manufactured by Orientec Co., Ltd. was used to obtain a stress-strain curve of each of the multicomponent fiber and the ultrafine fiber under the conditions of a sample length of 20 cm and a tension speed of 100%/min. The load at rupture was measured, and the load was divided by the initial fineness to calculate the strength. The strain at rupture was measured, and divided by the sample length to calculate the elongation. Evaluations were performed with a unit of cN/dtex for the strength and a unit of % for the elongation. For each of the strength and elongation, the above-mentioned procedure was repeated 5 times for each level, and the simple average of the obtained results was determined. The strength was rounded off to the first decimal place, and the elongation was rounded off to an integer.

E. Parameters

(multicomponent fiber diameter D, multicomponent fiber cross-section area Ac, island component maximum diameter d, inter-island component distance W, sea component region width H, sea component region length L, sea component region total cross-section area As, and neighboring island component parallelization degree θ) in cross-section observation of multicomponent fiber.

The obtained sea-island multicomponent fiber was embedded in an epoxy resin, the embedded sample was frozen by Cryosectioning System Model FC-4E manufactured by Reichert, and cut by Reichert-Nissei Ultracut N equipped with a diamond knife, and the cross section of the multicomponent fiber was then photographed using a scanning electron microscope (SEM) Model VE-7800 manufactured by KEYENCE CORPORATION.

The multicomponent fiber diameter D, the island component maximum diameter d, the inter-island component distance W, the sea component region width H, the sea component region length L and neighboring island component parallelization degree θ) were evaluated from randomly selected images using image processing software (WINROOF).

For the island component maximum diameter d, an image was photographed at a magnification allowing 150 or more island components to be observed, and island component diameters of 150 island components randomly extracted from the photographed image were measured. The value of the island component diameter is measured to the first decimal place in a unit of nm, and rounded off to an integer. The diameters of the 150 photographed island components were measured, and the maximum value thereof was defined as the island component maximum diameter d.

The multicomponent fiber diameter D, the inter-island component distance W, the sea component region width H and the sea component region length L were each measured to the second decimal place in a unit of μm from the cross-section image for randomly selected 10 or more multicomponent fibers in multifilaments, and the measured value was rounded off to the first decimal place. The above procedure was carried out for 10 or more spots, and the simple number average thereof was determined. From the thus obtained multicomponent fiber diameter D, sea component region width H and sea component region length L, the multicomponent fiber cross-section area Ac and the sea component region total cross-section area As per multicomponent fiber were determined.

The neighboring island component parallelization degree is an index showing the regularity of arrangement of island components. An angle θ formed by straight lines connecting the centers of two neighboring island components (45-(a) (straight line 1 connecting the centers of two island components) and 45-(b) (straight line 2 connecting the centers of other two island components) in FIG. 19) in four island components close to one another as illustrated in FIG. 19 was defined as the neighboring island component parallelization degree. Measurement was performed for 10 or more spots for each of randomly selected 10 or more multicomponent fibers in multifilaments, and the simple number average thereof was determined.

F. Sea Polymer Solubility

This item is intended to evaluate an effect of existence of a sea component region. The multicomponent fiber obtained under each of the spinning conditions was woven, and the obtained woven fabric was immersed for 15 minutes in a sea removal bath filled with a 3 wt % aqueous sodium hydroxide solution of 80° C. (bath ratio: 1:100 (woven fabric:solvent)) so that a sea polymer was removed. The bath ratio herein means the mass ratio of the sample to the solvent, and the bath ratio of 1:100 means that the removal treatment is performed using a solvent with a mass that is 100 times as large as the mass of a sample.

After the sea polymer was removed, water was removed, and the sample subjected to the removal treatment was dried in a hot air dryer at 60° C. The mass of the sample was measured at a temperature of 25° C. and a humidity of 55% RH before and after the elution treatment, and the weight reduction rate (%) was calculated in accordance with the equation described below. From the calculated weight reduction rate, sea polymer solubility of the multicomponent fiber was evaluated in three ranks as described below.

Weight reduction rate (%)=(1−weight of sample after elution treatment/weight of sample before elution treatment)×100

Evaluation of Sea Polymer Solubility

Very Good: The weight reduction rate is in the range of the sea polymer ratio (%)±5(%).

Good: The weight reduction rate is in the range of −5(%) to −10(%) of the sea polymer ratio (%).

Poor: The weight reduction rate is not more than −10(%) of the sea polymer ratio (%).

G. Evaluation of Coming-Off of Ultrafine Fiber (Island Component) During Sea Removal Treatment

The multicomponent fiber obtained under each of the spinning conditions was woven, 10 g of the obtained knitted fabric was prepared, and 99% or more of the sea polymer was removed in a removal bath filled with a 3 wt % aqueous sodium hydroxide solution of 80° C. (bath ratio: 1:100).

The bath ratio herein means the mass ratio of the sample to the solvent, and the bath ratio of 1:100 means that the sea removal treatment is performed using a solvent with a mass that is 100 times as large as the mass of a sample. Removal of the sea component is evaluated based on the weight reduction rate of the sample on the premise that the removal rate of the sea component and the weight reduction rate of the sample (equation described below) are the same value.

Weight reduction rate (%)=(1−weight of sample after elution treatment/weight of sample before elution treatment)×100

To evaluate the degree of coming-off of the ultrafine fiber, evaluation was performed as described below.

A 100 ml portion was sampled from the solution used for the sea removal treatment, and this solution was passed through glass fiber filter paper with a retained particle diameter of 0.5 μm. Based on the difference in dry mass of the filter as measured in an atmosphere at a temperature of 25° C. and a humidity of 55% RH between before and after the treatment, the degree of coming-off of the ultrafine fiber was evaluated in four ranks as described below.

Evaluation of Coming-Off of Ultrafine Fiber

Very Good: The mass difference is less than 3 mg.

Good: The mass difference is not less than 3 mg and less than 7 mg.

Fair: The mass difference is not less than 7 mg and less than 10 mg.

Bad: The mass difference is not less than 10 mg.

Example 1

Polyethylene terephthalate (PET, melt viscosity: 120 Pa·s) with an intrinsic viscosity (IV) of 0.63 dl/g as an island polymer, and PET (hereinafter referred to as “copolymer PET 1,” melt viscosity: 140 Pa·s) with an IV of 0.58 dl/g, which was copolymerized with 5.0 mol % of 5-sodium sulfoisophthalic acid, as a sea polymer were separately melted at 290° C., then weighed, and fed into a spinning pack containing a composite spinneret 7 of the example as shown in FIG. 2 so that a sea-island composite polymer flow was melt-discharged. The sea-island component ratio based on the mass of the fed polymer per unit time was 50/50. The discharged composite polymer flow was cooled and solidified, then supplied with an oil, and wound up at a spinning velocity of 1500 m/min to obtain an as-spun fiber of a 150 dtex-15 filament (single hole through-put rate: 2.25 g/min).

The wound-up as-spun fiber was drawn at a ratio of 3.0 between rollers heated to 90° C. and 130° C., respectively, to form a multicomponent fiber of a 50 dtex-15 filament. In Example 1, a distribution type spinneret as shown in FIG. 6 was used. In a nozzle plate 2, holes corresponding to the condition (i) were arranged to form a hexagonal lattice as illustrated in FIG. 28 so that the hole packing density was 1.5 (holes/mm²). The radius of a circumscribed circle of a nozzle hole collection was defined as “radius R”. (The “radius R” has the same meaning hereinafter.)

In the nozzle plate used in Example 1, sea component region forming hole groups were arranged from the outer periphery of the circumscribed circle of the nozzle hole collection to the circumference with a radius of 0.7R such that four sea component region forming hole groups were between sea-island discharge hole groups.

As shown in Table 1, four sea component regions 44 as illustrated in FIG. 14 were formed on the cross section of the obtained multicomponent fiber. The result of the cross-section observation showed that a multicomponent fiber was obtained as shown in Table 1. The obtained multicomponent fiber had mechanical properties acceptable in terms of high-order processability, with the strength being 2.5 cN/dtex and the elongation being 34%. Sea polymer solubility was satisfactory (Good). Since the efficiency during sea removal processing was improved as described above, the ultrafine fiber had excellent mechanical properties (strength: 2.4 cN/dtex and elongation: 45%) so that the degree of coming-off of the ultrafine fiber during sea removal was low (evaluation of coming-off: Good). Spinning conditions and results of evaluation of the multicomponent fiber and the ultrafine fiber are shown in Table 1.

Example 2

The same procedure as in Example 1 was carried out except that a composite spinneret was used which included a nozzle plate in which as illustrated in FIG. 29, island discharge holes 13 and sea discharge holes 12 were arranged to form a tetragonal lattice, the hole packing density was 2.0 (holes/mm²), and similarly to Example 1, some of sea-island discharge hole groups between four sea component region forming hole groups.

In Example 2, sea component regions were formed on the composite cross section similarly to Example 1, and thus sea component solubility was satisfactory (sea component solubility: Good) so that the degree of coming-off of the ultrafine fiber during sea removal was low (evaluation of coming-off: Good). Spinning conditions and results of evaluation of the multicomponent fiber and the ultrafine fiber are shown in Table 1.

Example 3

Except that a composite spinneret was used which included a nozzle plate as illustrated in FIG. 30 in which island discharge holes 13 were arranged to form a trigonal lattice, sea discharge holes 12 were arranged, the hole packing density was 3.0 (holes/mm²), and similarly to Example 1, four sea component region forming hole groups were arranged to surround some of sea-island discharge hole groups on both sides, the same procedure as in Example 1 was carried out to obtain a multicomponent fiber.

The cross section of the multicomponent fiber of Example 3 had four sea component regions as illustrated in FIG. 14. In cross-section observation, these sea component regions extended toward the center from the upper side, the right side, the lower side and the left side on the surface of the fiber, but did not reach the center. The shape thereof was almost rectangular. The cross-sectional parameter of the multicomponent fiber was as shown in Table 1, and satisfied the requirement of the multicomponent fiber. In Example 3, satisfactory sea component solubility comparable to sea component solubility in Examples 1 and 2 (sea component solubility: Good) was achieved although the island packing density was further increased and, further, the degree of coming-off of the ultrafine fiber during sea removal was also low (evaluation of coming-off: Good) although the diameter of the ultrafine fiber was reduced. Spinning conditions and results of evaluation of the multicomponent fiber and the ultrafine fiber are shown in Table 1.

Example 4

Except that a composite spinneret used in Example 4 was a pipe type spinneret as shown in FIG. 10, and included a nozzle plate as shown in FIG. 31, and the hole packing density was 1.2 (holes/mm²), the same procedure as in Example 1 was carried out to obtain a multicomponent fiber.

The multicomponent fiber of Example 4 had four sea component regions formed on the cross section as illustrated in FIG. 14. The cross-sectional parameter of the multicomponent fiber was as shown in Table 1, and satisfied the requirement of the multicomponent fiber. In Example 4, the fiber had satisfactory sea component solubility (sea polymer solubility: Good), but island components in the sea-island region were arranged in closest packing, and thus it took a little longer time to complete sea removal as compared to Example 1. Therefore, the degree of coming-off of the ultrafine fiber during sea removal tended to slightly increase, but remained at an acceptable level (evaluation of coming-off: Fair). Probably due to this, mechanical properties of the ultrafine fiber were slightly poorer as compared to Example 1, but remained at a practically acceptable level (strength 1.8 cN/dtex and elongation: 37%). Spinning conditions and results of evaluation of the multicomponent fiber and the ultrafine fiber are shown in Table 1.

Example 5

Except that a composite spinneret was used which included a nozzle plate in which as shown in FIG. 12, sea component region forming hole groups were arranged to reach the circumference with a radius of 0.5R, and the hole packing density was 1.4 (holes/mm²), the same procedure as in Example 1 was carried out to obtain a multicomponent fiber.

The multicomponent fiber of Example 5 had four sea component regions on the cross section as illustrated in FIG. 14. The cross-sectional parameter of the multicomponent fiber was as shown in Table 1, and satisfied the requirement of the multicomponent fiber. In Example 5, sea component region forming hole groups were arranged to reach the circumference with a radius of 0.5R and, therefore, as compared to Example 1, the sea component region extended to the inner part of the multicomponent fiber so that sea component solubility was extremely excellent (sea component solubility: Very Good) although the ratio (H/D) of the multicomponent fiber diameter D to the sea component region width H was 0.03, a value comparable to that in Example 1. The sample of Example 5 was treated for 5 minutes under the same sea removal treatment conditions as in the evaluation of sea polymer solubility, an ultrafine fiber bundle of the treated sample was observed, and the result of the observation showed that the multicomponent fiber was divided into a plurality of parts due to formation of cracks in the multicomponent fiber. This effect is ascribable to improvement of sea component solubility. Since the treatment time required for completing sea removal was shortened, coming-off of the ultrafine fiber hardly occurred (evaluation of coming-off: Very Good), and the ultrafine fiber had excellent strength characteristics (strength: 2.6 cN/dtex and elongation: 57%). Spinning conditions and results of evaluation of the multicomponent fiber and the ultrafine fiber are shown in Table 1.

Example 6

Except that the island polymer ratio was 80%, the same procedure as in Example 1 was carried out to obtain a multicomponent fiber.

The multicomponent fiber of Example 6 had four sea component regions on the cross section as illustrated in FIG. 14. The cross-sectional parameter of the multicomponent fiber was as shown in Table 1, and satisfied the requirement of the multicomponent fiber. In Example 6, the mechanical properties of the multicomponent fiber were significantly improved (strength: 3.3 cN/dtex and elongation: 31%) as compared to Example 1 by increasing the island polymer ratio. In Example 6, fiber breakage did not occur during a Spinning step such as spinning and drawing, and a step of processing the fiber into a fabric, and thus excellent quality was achieved. Although the island polymer ratio was increased to 80%, sea polymer solubility was satisfactory (sea polymer solubility: Good) owing to the effect of the sea component region as a feature. Besides such satisfactory sea polymer solubility, the fiber structure of the island component was highly formed in the Spinning step so that coming-off of the ultrafine fiber during sea removal did not occur (evaluation of coming-off: Very Good), and the ultrafine fiber had excellent mechanical properties (strength: 3.1 cN/dtex and elongation: 40%). Spinning conditions and results of evaluation of the multicomponent fiber and the ultrafine fiber are shown in Table 1.

Example 7

Except that the island polymer ratio was 20%, the same procedure as in Example 1 was carried out to obtain a multicomponent fiber.

The multicomponent fiber of Example 7 had four sea component regions on the cross section as illustrated in FIG. 14. The cross-sectional parameter of the multicomponent fiber was as shown in Table 1, and satisfied our requirement of the multicomponent fiber. In Example 7, the island polymer ratio was reduced, and thus the ratio (H/D) of the multicomponent fiber diameter D to the sea component region width H increased to 0.25 so that sea component solubility was extremely excellent (sea component solubility: Very Good). Similarly to Example 5, the sample was treated for 5 minutes under the same elution treatment conditions as in the evaluation of sea component solubility, an ultrafine fiber bundle of the treated sample was observed, and the result of the observation showed that the multicomponent fiber was already divided into a plurality of parts, and ultrafine fibers were already generated at many parts. On the other hand, probably due to insufficient formation of the fiber structure of the island component because the island polymer ratio was set a low value in the ultrafine fiber, the degree of coming-off of the ultrafine fiber slightly increased as compared to Example 1, but remained at a practically acceptable level (evaluation of coming-off: Fair). Spinning conditions and results of evaluation of the multicomponent fiber and the ultrafine fiber are shown in Table 1.

Comparative Example 1

Except that a composite spinneret was used which included a nozzle plate in which island discharge holes and sea discharge holes were arranged to form a hexagonal lattice similarly to Example 1, and a sea component region forming hole group was not arranged, the same procedure as in Example 1 was carried out to obtain a multicomponent fiber.

In the multicomponent fiber of Comparative Example 1, the cross section thereof was not provided with a sea component region as a feature because a sea component region forming hole group was not arranged, and thus the same sea-island multicomponent fiber as conventional one as illustrated in FIG. 27 was obtained.

In Comparative Example 1, mechanical properties were almost comparable to those in Example 1 (strength: 2.3 cN/dtex and elongation: 32%), but since elution of the sea polymer gradually proceeded from the outermost layer of the multicomponent fiber, sea component solubility was considerably reduced (sea component solubility: Poor). Similarly to Example 5, the sample of Comparative Example 1 was treated for 5 minutes under the same elution treatment conditions as in the evaluation of sea component solubility, an ultrafine fiber bundle of the treated sample was observed, and the result of the observation showed that only the sea component on the surface layer of the multicomponent fiber was removed, and sea removal hardly proceeded. Accordingly, for the sample of Comparative Example 1, it was required to considerably extend the time to complete sea removal, and resultantly island components arranged in the vicinity of the outermost layer of the multicomponent fiber were also treated with a solvent so that coming-off of the ultrafine fiber frequently occurred (evaluation of coming-off: Bad). Therefore, the ultrafine fiber had much lower mechanical properties (strength: 1.8 cN/dtex and elongation: 16%) as compared to Example 1, and observation of the resulting ultrafine fiber bundle showed small pieces of fuzzed ultrafine fiber, and thus the ultrafine fiber was not satisfactory in quality. Spinning conditions and results of evaluation of the multicomponent fiber and the ultrafine fiber are shown in Table 1.

TABLE 1 Compar- ative Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- ple 1 ple 2 ple 3 ple 4 ple 5 ple 6 ple 7 ple 1 Spinning Sea component PET PET PET PET PET PET PET PET conditions Island component Coplymer Coplymer Coplymer Coplymer Coplymer Coplymer Coplymer Coplymer PET1 PET1 PET1 PET1 PET1 PET1 PET1 PET1 Ratio of sea [%] 50 50 50 50 50 20 80 50 Ratio of island [%] 50 50 50 50 50 80 20 50 n-gonal lattice 6 4 3 — 6 6 6 6 Hole packing density [Holes/mm²] 1.5 2.0 3.0 1.2 1.4 1.5 1.5 1.5 Spinning velocity [m/min] 1500 1500 1500 1500 1500 1500 1500 1500 Stretch ratio [—] 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 Result of Existence of sea Yes Yes Yes Yes Yes Yes Yes No cross-section component region observation D: Diameter of [μm] 68 68 68 68 68 68 68 68 of multi- multicomponent fiber component d: Maximum diameter [nm] 784 679 555 877 812 992 496 784 fiber of island compone

W: Maximam distance [nm] 90 70 50 120 100 30 190 100 of neighboring isla

L/D [—] 0.15 0.15 0.15 0.15 0.25 0.15 0.15 — H/D [—] 0.03 0.025 0.01 0.015 0.03 0.001 0.25 — As/Ac [—] 0.023 0.019 0.008 0.011 0.038 0.000 0.191 — θ: Neighboring [°] 2 3 1 22 0 2 5 1 island component parallelization degree Property of Fineness [dtex] 50 50 50 50 50 50 50 50 multi- Strength [cN/dtex] 2.5 2.4 2.2 1.9 2.7 3.3 2.0 1.9 component Elongation [%] 34 31 35 28 43 30 21 32 fiber Sea polymer solubility [—] Good Good Good Good Very Good Very Poor Good Good Evaluated coming-off [—] Good Good Good Fair Very Very Fair Bad Good Good Ultrafine Fineness [dtex] 25 25 25 25 25 40 10 25 fiber Strength [cN/dtex] 2.4 2.3 2.1 1.8 2.6 3.1 1.9 1.8 Elongation [%] 45 41 46 37 57 40 27 16

indicates data missing or illegible when filed

Comparative Example 2

Except that a composite spinneret was used which included a nozzle plate in which island discharge holes and sea discharge holes were arranged to form a hexagonal lattice similarly to Example 1, a sea component region forming hole group was not arranged, and the hole packing density was 3.0 (holes/mm²), and the island polymer ratio was 80%, the same procedure as in Example 1 was carried out to obtain a multicomponent fiber.

In the multicomponent fiber of Comparative Example 2, the cross section thereof was not provided with a sea component region as a feature because a sea component region forming hole group was not arranged, and the number of islands increased by a factor of 2 as compared to Comparative Example 1 so that the multicomponent fiber had a cross-section structure in which the whole cross section thereof was closely packed with the island component.

In Comparative Example 2, the multicomponent fiber had relatively satisfactory mechanical properties (strength: 3.3 cN/dtex and elongation: 33%), but the fiber had a structure in which the island component was densely arranged so that elution of the sea polymer was extremely hard to proceed, leading to extremely low sea component solubility (sea component solubility: Poor). Similarly to Example 5, the sample of Comparative Example 2 was treated for 5 minutes under the same elution treatment conditions as in the evaluation of sea component solubility, a fiber bundle of the sample was observed, and the result of the observation showed that elution of the sea polymer hardly proceeded, and the state of the multicomponent fiber was almost unchanged from the state before the treatment. Since ultrafine fibers were in part generated in Comparative Example 1, the sea component solubility of the sample of Comparative Example 2 was further reduced as compared to Comparative Example 1.

Accordingly, for the sample of Comparative Example 2, only a multicomponent fiber with a sea polymer remaining therein was obtained although the sea removal time was extended, and thus the treatment with an aqueous sodium hydroxide solution was stopped 2 hours after the start of the treatment. Coming-off of the ultrafine fiber was examined, and the result of the examination showed that coming-off frequently occurred (evaluation of coming-off: Bad). The mechanical properties of the sample treated for 2 hours were examined for reference, and the result of the examination showed that the sample had very low mechanical properties and was not satisfactory in quality. Spinning conditions and results of evaluation of the multicomponent fiber and the ultrafine fiber are shown in Table 2.

Comparative Example 3

Except that a pipe type spinneret as illustrated in FIG. 10 was used which included a nozzle plate in which a sea component region forming hole group was not arranged, the same procedure as in Example 1 was carried out to obtain a multicomponent fiber.

The multicomponent fiber of Comparative Example 3 was not provided with a sea component region as a feature similarly to Comparative Example 1, had the island component arranged concentrically from the center of the multicomponent fiber as compared to Example 1, and had a neighboring island component parallelization degree θ of 25°.

The multicomponent fiber of Comparative Example 3 had no particular problem in the spinning step, but suffered frequent thread breakage in the drawing step. On the other hand, the mechanical properties of the multicomponent fiber, although varied, were satisfactory (strength: 2.5 cN/dtex and elongation: 38%), and due to a large inter-island component distance, sea component solubility was acceptable (sea component solubility: Good). However, as described above, since the quality of the multicomponent fiber was not satisfactory, and also the arrangement of the island component was not a regular arrangement as in our fibers, there was a limit on enhancement of the fiber structure of the island component, and coming-off of the ultrafine fiber frequently occurred at the time when sea removal was completed (evaluation of coming-off: Bad). Therefore, the ultrafine fiber had much lower mechanical properties (strength: 1.5 cN/dtex and elongation: 13%) as compared to Example 1, and was poor in quality. Spinning conditions and results of evaluation of the multicomponent fiber and the ultrafine fiber are shown in Table 2.

Comparative Example 4

Except that the same pipe type spinneret as that in Comparative Example 3, which included a nozzle plate in which a sea component region forming hole group was not arranged, was used, and the island polymer ratio was 70%, the same procedure as in Example 1 was carried out to obtain a multicomponent fiber. In Comparative Example 4, spinning was performed with the island polymer ratio set to 80%, but island components were fused together to collapse the composite cross section and, therefore, spinning was performed with the island polymer ratio reduced to 70%.

The multicomponent fiber of Comparative Example 4 was not provided with a sea component region as a feature similarly to Comparative Example 3, and had the island component densely arranged on the cross section of the multicomponent fiber because the island polymer ratio was increased as compared to Comparative Example 3. The neighboring island component parallelization degree θ was 17°.

The mechanical properties of the multicomponent fiber of Comparative Example 4, although varied similarly to Comparative Example 3, were relatively satisfactory (strength: 2.8 cN/dtex and elongation: 31%), but since the island component was densely arranged, the sea removal did not efficiently proceed, and even as compared to Example 6 where the island polymer ratio was higher by 10%, sea component solubility was reduced (sea component solubility: Poor). Therefore, in the multicomponent fiber of Comparative Example 4, the time required for the sea removal treatment was twice or more as long as that in Example 6, and coming-off of the ultrafine fiber frequently occurred (evaluation of coming-off: Bad). Therefore, the ultrafine fiber had reduced quality with the fiber having fuzzes and also had much lower mechanical properties (strength: 1.7 cN/dtex and elongation: 18%) as compared to Example 6. The results are shown in Table 2.

Comparative Example 5

A composite spinneret was used which included a nozzle plate 11 in which island component pipe groups were arranged to form an equilateral-triangular lattice, and as illustrated in FIG. 17, composite polymer discharge holes 15 existed, and sea polymer admission channels (having no discharge holes) were provided, the composite spinneret being the same pipe type spinneret as that in Comparative Example 3 in which a sea component region forming hole group was not arranged. Further, the island polymer ratio was 80%. This condition was based on the method disclosed in Japanese Patent Laid-open Publication No. 2009-91680. Except that the above-described condition was employed, the same procedure as in Example 1 was carried out to obtain a multicomponent fiber.

In Comparative Example 5, spinning was performed with the island polymer ratio set to 80%, but fusing of island components was suppressed so that a sea-island composite cross section was successfully formed.

However, in Comparative Example 5, a sea component region forming hole group as we use is not provided. Therefore, a sea component region as a feature was not formed, and the island component was densely formed over the entire region of the composite cross section. The neighboring island component parallelization degree θ was 23°.

However, in the multicomponent fiber of Comparative Example 5, the sea removal did not proceed probably because the island component was densely arranged, and sea polymer solubility was much lower as compared to Example 6 (sea polymer solubility: Poor). Therefore, in Comparative Example 5, similarly to Comparative Example 4, the time required for the sea removal treatment was twice or more as long as that in Example 6, and coming-off of the ultrafine fiber frequently occurred. In observation of the sample after sea removal, a sea polymer portion partially existed at the central part of the multicomponent fiber, and thus removal sea was not completed in some parts. The ultrafine fiber bundle of Comparative Example 5 had a poor texture with the fiber having fuzzes In Comparative Example 5, mechanical properties were also much lower as compared to Example 6 (strength: 1.9 cN/dtex and elongation: 12%). Spinning conditions and results of evaluation of the multicomponent fiber and the ultrafine fiber are shown in Table 2.

TABLE 2 Comparative Comparative Comparative Comparative Example 2 Example 3 Example 4 Example 5 Spinning Sea component PET PET PET PET conditions Island component Coplymer Coplymer Coplymer Coplymer PET1 PET1 PET1 PET1 Ratio of sea [%] 20 50 30 20 Ratio of island [%] 80 50 70 80 n-gonal lattice 6 — — — Hole packing density [Holes/mm²] 3.0 1.5 1.5 1.5 Spinning velocity [m/min] 1500 1500 1500 1500 Stretch ratio [—] 3.0 3.0 3.0 3.0 Result of Existence of sea No No No No cross-section component region observation D: Diameter of [μm] 68 68 68 68 of multi- multicomponent fiber component d: Maximum diameter [nm] 701 784 928 928 of island components fiber W: Maximam distance [nm] 20 100 50 20 of neighboring islands L/D [—] — — — — H/D [—] — — — — As/Ac [—] — — — — θ: Neighboring [°] 0 25 17 23 island component parallelization degree Property of Fineness [dtex] 50 50 50 50 multi- Strength [cN/dtex] 3.6 2.5 2.8 3.3 component Elongation [%] 33 38 31 35 fiber Sea polymer solubility [—] Poor Good Poor Poor Evaluated coming-off [—] Bad Bad Bad Bad Ultrafine Fineness [dtex] 40 25 35 35 fiber Strength [cN/dtex] 1.1 1.5 1.7 1.9 Elongation [%] 13 13 18 12

Examples 8 to 10

A composite spinneret was used which included a nozzle plate in which the number of holes in the sea component region forming hole group in the nozzle plate illustrated in FIG. 28 and used in Example 6 was increased by a factor of 3 (Example 8), by a factor of 10 (Example 9) and by a factor of 40 (Example 10) in the shaded regions in FIG. 28 to change the sea component region width H. Further, the island polymer ratio was changed as shown in Table 3 to adjust the inter-island component distance. Except that the above-described changes were made, the same procedure as in Example 6 was carried out to obtain a multicomponent fiber.

In each of the multicomponent fibers of Examples 8 to 10, four sea component regions were formed as illustrated in FIG. 14, but since the number of holes in the sea component region forming hole group was changed, the sea component region width H increased as compared to Example 6.

In each of the examples, the multicomponent fiber had excellent mechanical properties with the strength being 3.2 cN/dtex or more and the elongation being 29% or more. In not only the Spinning step but also woven fabric processing to evaluate sea component solubility, thread breakage and fuzzing did not occur, and thus the fabric had excellent quality.

As compared to Example 6, sea component solubility tended to be improved as the size of the sea component region increased, and particularly in Examples 9 and 10, the multicomponent fiber had extremely excellent performance, and similarly to Example 5, ultrafine fibers were already generated in a sample obtained through the treatment performed for 5 minutes.

Therefore, in the multicomponent fiber of each of Examples 8 to 10, the time required for completely removing the sea polymer was reduced. Therefore, the degree of coming-off of the ultrafine fiber was low (evaluation of coming-off: Very Good), and the ultrafine fiber had excellent mechanical properties. The results are shown in Table 3.

Examples 11 and 12

A composite spinneret was used which included, in place of the nozzle plate used in Example 5, a nozzle plate provided with eight sea component region forming hole groups which extended inward from the outer layer and which were absent at the center. The island polymer ratio was 70%. Except that the above-described changes were made, the same procedure as in Example 5 was carried out to obtain a multicomponent fiber (Example 11).

In Example 12, spinning was carried out at a stretch ratio of 1.7 under the same spinning conditions as in Example 11 except that the spinning velocity was changed to 3000 m/min.

In each of Examples 11 and 12, eight sea component regions were formed as illustrated in FIG. 20. From comparison with the cross section in Example 5, it was confirmed that a composite cross section was formed in which the number of sea component regions was increased from 4 to 8 while the size of the sea component region was comparable (L/D: 0.25 and H/D: 0.03). In each of Examples 11 and 12, there was no problem in the Spinning step, and particularly in Example 12, thread breakage was not noticeable although the spinning velocity was increased by a factor of 2 to 3000 m/min.

For the samples of Examples 11 and 12, sea component solubility was satisfactory (sea component solubility: Good) due to an increase in the number of sea component regions, and ultrafine fibers generated from the multicomponent fibers had excellent mechanical properties. The results are shown in Table 3.

Examples 13 and 14

In place of the spinneret used in Example 1, a composite spinneret was used which included a nozzle plate in which sea component region forming hole groups were arranged to extend across the nozzle hole collection while orthogonally crossing each other as shown in FIG. 5. Except that the above-described change was made, the same procedure as in Example 11 was carried out to obtain a multicomponent fiber (Example 13). In Example 14, spinning was carried out at a stretch ratio of 1.7 under the same spinning conditions as in Example 13 except that the spinning velocity was changed to 3000 m/min.

In each of Examples 13 and 14, sea component regions were formed to extend across the cross section of the multicomponent fiber and orthogonally cross each other at the center of the multicomponent fiber as shown in FIG. 13 (L/D: 1.00). In Examples 13 and 14, the area ratio of the sea component region increased at the multicomponent fiber cross section with the ratio As/Ac being 0.153 while the sea component region width (H/D: 0.03) was comparable to that in Example 11, and sea component solubility of the multicomponent fiber was further improved as compared to Example 11 (sea component solubility: Very Good).

In the multicomponent fibers of Examples 13 and 14, the multicomponent fiber was observed to be divided into a plurality of parts for samples treated with an aqueous sodium hydroxide solution for 5 minutes similarly to Example 5. In these multicomponent fibers, cracks were formed on sea component regions arranged to extend across the cross section of the fiber. Therefore, the multicomponent fiber was divided into a plurality of parts in the initial stage of sea removal in the sea removal treatment. Owing to this effect, the treatment time to complete sea removal was reduced although the multicomponent fiber had a relatively high island polymer ratio of 70% in the multicomponent fibers of Examples 13 and 14. Accordingly, coming-off of the ultrafine fiber was hardly observed (evaluation of coming-off: Very Good). The results are shown in Table 3.

Example 15

In place of the nozzle plate used in Example 13, a nozzle plate was provided in which sea component region forming hole groups continuously arranged to extend across the nozzle hole collection 18 were added and evenly arranged as shown in FIG. 32. Except that a composite spinneret was used which included a nozzle plate as illustrated in FIG. 32, the same procedure as in Example 13 was carried out to spin a multicomponent fiber. In Example 15, four sea component regions were arranged at intervals of 45° to extend across the cross section of the multicomponent fiber as shown in FIG. 21 (H/D: 0.03 and L/D: 1.00).

In Example 15, sea component regions extended through the cross section of the fiber to further divide the sea-island region so that in the initial stage of sea removal, the multicomponent fiber was easily divided into a plurality of parts, leading to an increase in apparent surface area exposed to an aqueous sodium hydroxide solution, and thus the multicomponent fiber had more satisfactory sea component solubility as compared to Example 13 (sea component solubility: Very Good). As a result, the time required to complete sea removal was reduced as compared to comparative examples, and coming-off of the ultrafine fiber hardly occurred (evaluation of coming-off: Very Good). The results are shown in Table 3.

TABLE 3 Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- ple 8 ple 9 ple 10 ple 11 ple 12 ple 13 ple 14 ple 15 Spinning Sea component PET PET PET PET PET PET PET PET conditions Island component Coplymer Coplymer Coplymer Coplymer Coplymer Coplymer Coplymer Coplymer PET1 PET1 PET1 PET1 PET1 PET1 PET1 PET1 Ratio of sea [%] 20 25 30 30 30 30 30 30 Ratio of island [%] 80 75 70 70 70 70 70 70 n-gonal lattice 6 6 6 6 6 6 6 6 Hole packing density [Holes/mm²] 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Spinning velocity [m/min] 1500 1500 1500 1500 3000 1500 3000 1500 Stretch ratio [—] 3.0 3.0 3.0 3.0 1.7 3.0 1.7 3.0 Result of Existence of sea Yes Yes Yes Yes Yes Yes Yes Yes cross-section component region observation D: Diameter of [μm] 68 68 68 68 64 68 64 68 of multi- multicomponent fiber component d: Maximum diameter [nm] 992 961 928 928 872 928 872 928 fiber of island compon

W: Maximam distance [nm] 30 30 20 40 40 20 20 30 of neighboring is

L/D [—] 0.15 0.15 0.15 0.25 0.25 1.00 1.00 1.00 H/D [—] 0.050 0.100 0.200 0.030 0.030 0.030 0.030 0.010 As/Ac [—] 0.038 0.076 0.153 0.076 0.076 0.153 0.153 0.102 θ: Neighboring [°] 0 1 4 0 1 0 0 2 island component parallelization degree Property of Fineness [dtex] 50 50 50 50 44 50 44 50 multi- Strength [cN/dtex] 3.4 3.3 3.2 3.4 2.6 3.2 2.9 2.9 component Elongation [%] 29 29 33 33 22 29 31 37 fiber Sea polymer solubility [—] Good Very Very Good Good Very Very Very Good Good Good Good Good Evaluated coming-off [—] Very Very Very Very Good Very Very Very Good Good Good Good Good Good Good Ultrafine Fineness [dtex] 40 38 35 35 31 35 31 35 fiber Strength [cN/dtex] 3.2 3.1 3.0 3.2 2.5 3.0 2.8 2.8 Elongation [%] 38 38 43 44 29 38 41 49

indicates data missing or illegible when filed

Examples 17 and 18

A nozzle plate was provided in which as shown in FIG. 33, island discharge holes 13 and sea discharge holes 12 were arranged to form a tetragonal lattice, and the sea component region forming hole group was arranged over a range of 0.5R from the center of the nozzle hole collection 18 toward the outer layer (hole packing density: 1.5 holes/mm²). Except that a composite spinneret including this nozzle plate was used, and the sea polymer was PET copolymerized with 8.0 mol % of 5-sodium sulfoisophthalic acid with an IV of 0.50 dl/g (copolymer PET 2, melt viscosity: 120 Pa·s), the same procedure as in Example 6 was carried out to obtain a multicomponent fiber (Example 17).

Except that a nozzle plate 2 was used in which the hole packing density of the spinneret used in Example 17 was changed to 0.3 holes/mm², the same procedure as in Example 11 was carried out to perform spinning in Example 18. In each of Examples 17 and 18, sea component regions were formed to extend in eight directions from the center of the multicomponent fiber as shown in FIG. 22. Since the hole packing density was changed, the ratios H/D and As/Ac of the multicomponent fiber were changed as shown in Table 4 while the ratio L/D was 0.50. The multicomponent fiber of each of Examples 17 and 18 had cracks formed on the cross section thereof through the removal treatment performed for 5 minutes in the same manner as in Example 5 so that an aqueous sodium hydroxide solution infiltrated into the inner part of the multicomponent fiber in the initial stage of the sea removal treatment although the sea component region did not reach the outermost layer of the multicomponent fiber. Therefore, the multicomponent fiber of Example 18 had excellent sea component solubility (sea component solubility: Very Good) because the sea component region was widely formed, and the multicomponent fiber of Example 17 also had satisfactory sea component solubility (sea component solubility: Good) owing to the effect of crack formation as described above. The results are shown in Table 4.

Example 19

A nozzle plate was used in which removing sea discharge hole groups were arranged such that sea component regions were formed in a trapezoidal shape at the center of the multicomponent fiber as shown in FIG. 34, and the hole packing density was 0.3 holes/mm². The removing sea discharge hole groups were continuously arranged over a range of 0.4R from the center of the nozzle hole collection 18, with the sea component regions formed horizontally symmetrically in the multicomponent fiber. Except that a composite spinneret was used which included a nozzle plate as illustrated in FIG. 34, the same procedure as in Example 17 was carried out to obtain a multicomponent fiber.

In the multicomponent fiber of Example 19, trapezoidal sea component regions continuously extending in the circumferential direction (120°) as shown in FIG. 23 were formed on the cross section of the fiber depending on the arrangement of sea component region forming hole groups. In Example 19, the sea component region did not reach the outermost layer of the multicomponent fiber similarly to Example 18, but from observation of a sample similar to that of Example 5, which was subjected to a short-time sea removal treatment (5 minutes), it was found that cracks were formed on the cross section of the multicomponent fiber in the initial stage of sea removal. Therefore, sea component solubility was satisfactory (sea component solubility: Good), and the sea removal time was reduced so that coming-off of the ultrafine fiber at the time when sea removal was completed was suppressed (evaluation of coming-off: Good). The results are shown in Table 4.

Examples 20 and 21

Except that a composite spinneret was used which included a nozzle plate in which the range over which the removing sea discharge hole group in the nozzle plate illustrated in FIG. 34 was continuously extended to 0.5R from the center of the nozzle hole collection 18 to expand the sea component region formed at the center of the multicomponent fiber in view of the results of Example 19, the same procedure as in Example 19 was carried out to obtain a multicomponent fiber. In Example 21, spinning was carried out at a stretch ratio of 1.5 under the same spinning conditions as in Example 20 except that the spinning velocity was changed to 3000 m/min.

In the multicomponent fibers of Examples 20 and 21, due to expansion of the range over which the removing sea discharge hole group was arranged, the sea component region formed in the multicomponent fiber was expanded in comparison with Example 19 as illustrated in FIG. 24. In Example 20, due to expansion of the sea component region formed in the multicomponent fiber, crack formation and infiltration of an aqueous sodium hydroxide solution in the initial stage of sea removal were facilitated as compared to Example 19 so that the multicomponent fiber had excellent sea component solubility (sea component solubility: Very Good), and the treatment time required for completing sea removal was reduced so that coming-off of the ultrafine fiber was not observed (evaluation of coming-off: Very Good).

Therefore, the ultrafine fiber after sea removal had excellent mechanical properties, and the resulting ultrafine fiber bundle was free from fibrillation, and thus had excellent quality. In Example 21, thread breakage did not occur in the spinning step and the drawing step although the spinning velocity was increased, and thus the multicomponent fiber had satisfactory Spinning performance. In addition, cracks were formed in the multicomponent fiber in the initial stage of the sea removal treatment similarly to Example 19, and thus the multicomponent fiber was confirmed to have satisfactory sea component solubility (sea component solubility: Good).

Example 22

Except that a composite spinneret was used which included a nozzle plate in which removing sea discharge hole groups were arranged such that sea component regions orthogonally crossed one another at equal intervals on the cross section of the multicomponent fiber as illustrated in FIG. 35, the same procedure as in Example 11 was carried out to obtain a multicomponent fiber.

On the cross section of the multicomponent fiber of Example 22, sea component regions were formed at equal intervals while being between a sea-island region as illustrated in FIG. 26.

In Example 22, a plurality of cracks were apparently formed on the composite cross section in a short-time-treated sample similar to that of Example 5, and the sea-island region was divided into a plurality of parts. Owing to the effect of dividing the multicomponent fiber into a plurality of parts in the initial stage of the sea removal treatment, the specific surface area of the sea polymer exposed to an aqueous sodium hydroxide solution increased so that the multicomponent fiber had extremely excellent sea component solubility (sea component solubility: Very Good). Due to the above-mentioned effect, the treatment time taken for the sea polymer to be completely removed can be considerably reduced, coming-off of the ultrafine fiber hardly occurred during sea removal (evaluation of coming-off: Very Good), and the ultrafine fiber was free from fuzzes, and had excellent mechanical properties. The results are shown in Table 4.

Example 23

Except that a composite spinneret was used which included a nozzle plate in which removing sea discharge hole groups were arranged such that sea component regions were formed in a trigonal shape at the center of the multicomponent fiber as illustrated in FIG. 36, and the hole packing density was 0.3 holes/mm², the same procedure as in Example 19 was carried out to obtain a multicomponent fiber.

In the multicomponent fiber of Example 23, trigonal sea component regions as shown in FIG. 25 were formed on the cross section of the fiber depending on the arrangement of sea component region forming hole groups. In Example 23, the sea component region did not reach the outermost layer of the multicomponent fiber similarly to Example 19, but from observation of a sample similar to that of Example 5, which was subjected to a short-time sea removal treatment (5 minutes), we found that cracks were formed on the cross section of the multicomponent fiber in the initial stage of sea removal. Therefore, sea component solubility of the sample was satisfactory (sea component solubility: Very Good), and the sea removal time was reduced so that coming-off of the ultrafine fiber at the time when sea removal was completed was suppressed (evaluation of coming-off: Very Good). The results are shown in Table 4.

TABLE 4 Exam- Exam- Exam- Exam- Exam- Exam- Exam- ple 17 ple 18 ple 19 ple 20 ple 21 ple 22 ple 23 Spinning Sea component PET PET PET PET PET PET PET conditions Island component Coplymer Coplymer Coplymer Coplymer Coplymer Coplymer Coplymer PET2 PET2 PET2 PET2 PET2 PET1 PET2 Ratio of sea [%] 20 20 20 20 20 20 20 Ratio of island [%] 80 80 80 80 80 80 80 n-gonal lattice 4 4 4 4 4 4 4 Hole packing density [Holes/mm²] 1.5 0.3 0.3 0.3 0.3 1.5 0.3 Spinning velocity [m/min] 1500 1500 1500 1500 3000 1500 1500 Stretch ratio [—] 3.2 3.2 3.2 3.2 1.5 3.0 3.2 Result of Existence of sea Yes Yes Yes Yes Yes Yes Yes cross-section component region observation D: Diameter of [μm] 66 66 66 66 68 68 68 of multi- multicomponent fiber component d: Maximum diameter [nm] 961 2148 2148 2148 2218 992 2148 fiber of island component

W: Maximam distance [nm] 30 110 130 30 30 30 130 of neighboring islan

L/D [—] 0.50 0.50 0.10 0.13 0.13 0.83 0.25 H/D [—] 0.005 0.010 0.030 0.038 0.038 0.005 0.050 As/Ac [—] 0.025 0.051 0.027 0.167 0.167 0.021 0.125 θ: Neighboring [°] 3 0 4 5 4 2 3 island component parallelization degree Property of Fineness [dtex] 47 47 47 47 50 50 50 multi- Strength [cN/dtex] 4.2 3.8 3.7 4.2 3.4 3.7 3.0 component Elongation [%] 24 29 33 25 25 33 29 fiber Sea polymer solubility [—] Good Very Good Good Very Good Good Very Good Very Good Evaluated coming-off [—] Very Good Very Good Good Very Good Good Very Good Very Good Ultrafine Fineness [dtex] 38 38 38 38 40 40 40 fiber Strength [cN/dtex] 4.0 3.6 3.5 4.0 3.2 3.5 3.2 Elongation [%] 31 38 43 33 33 43 38

indicates data missing or illegible when filed 

1.-21. (canceled)
 22. A multicomponent fiber comprising a sea component and an island component, wherein, in cross-section observation of the multicomponent fiber, the multicomponent fiber comprises: a sea-island region with the plurality of island components arranged in the sea component; and one or more sea component regions formed only of the sea component between the sea-island region, and a width (H) of the sea component region is larger than a maximum value of a distance (W) between island components existing in the sea-island region and neighboring each other.
 23. The multicomponent fiber according to claim 22, wherein the sea component region extends inwardly from a surface layer of the multicomponent fiber.
 24. The multicomponent fiber according to claim 23, wherein the island components in the sea-island region are regularly arranged.
 25. The multicomponent fiber according to claim 22, wherein in cross-section observation of the sea-island multicomponent fiber, a ratio (L/D) of a length (L) of the sea component region to a diameter (D) of the multicomponent fiber is 0.25 or more.
 26. The multicomponent fiber according to claim 22, wherein in cross-section observation of the sea-island multicomponent fiber, the width (H) of the sea component region is larger than the maximum diameter (d) of the island component.
 27. The multicomponent fiber according to claim 26, wherein in cross-section observation, there exists at least one sea component region where the width (H) of the sea component region is larger than the maximum diameter (d) of the island component, and the length (L1) of the sea component region is equal to or larger than ¼ of the diameter (D) of the multicomponent fiber.
 28. The multicomponent fiber according to claim 27, wherein in cross-section observation, the cross-section area (Ac) of the multicomponent fiber and the sum of areas (As) of sea component regions satisfy: 0.05≦As/Ac≦0.35.
 29. The multicomponent fiber according to claim 22, wherein in cross-section observation, the sea component region is cruciform.
 30. A composite spinneret that discharges a composite polymer composed of an island polymer and a sea polymer, the composite spinneret satisfying (1) and (2): (1) the composite spinneret comprises: a distribution device that distributes polymers; a nozzle plate situated on a downstream side of the distribution device in a polymer spinning passage direction and which has a plurality of sea discharge holes, and at least one kind of discharge holes selected from a plurality of island discharge holes and a plurality of composite polymer discharge holes; and a flow contraction plate situated on the downstream side of the nozzle plate in the polymer spinning passage direction and which has a introducting hole communicating with discharge holes in a combination of discharge holes selected from the combinations of: the sea discharge holes and the island discharge holes; the sea discharge holes and the composite polymer discharge holes; and the sea discharge holes, the island discharge holes and the composite polymer discharge holes; and (2) the nozzle plate has a nozzle hole collection including a plurality of discharge holes, and the nozzle hole collection includes a sea component region forming hole group including the sea discharge holes, and at least one sea-island discharge hole group including any of (i) to (v): (i) the sea discharge holes and the island discharge holes; (ii) the composite polymer discharge holes; (iii) the sea discharge holes and the composite polymer discharge holes; (iv) the island discharge holes and the composite polymer discharge holes; and (v) the sea discharge holes, the island discharge holes and the composite polymer discharge holes.
 31. The composite spinneret according to claim 30, wherein the composite spinneret further satisfies (3): (3) the sea component region forming hole group is continuously arranged inwardly from an outer periphery of the nozzle hole collection with a part of the sea-island discharge hole group held between both sides.
 32. The composite spinneret according to claim 30, wherein the distribution device has a plurality of composite polymer discharge holes, and comprises: a plurality of pipes that supply the island polymer to the polymer discharge hole, the pipes arranged at positions corresponding to the composite polymer discharge holes of the nozzle plate on a one-to-one basis; a sea polymer introduction channel that supplies the sea polymer; and a sea polymer distribution chamber provided to communicate with the sea polymer introduction channel and surround the plurality of pipes, and the composite polymer discharge hole of the nozzle plate communicates with the pipe and the sea polymer distribution chamber.
 33. The composite spinneret according to claim 31, wherein the sea component region forming hole group is continuously arranged from an outer periphery of a circumscribed circle of the nozzle hole collection having a radius of R to the inside of a circle having a radius of 0.5R or less from the center with the sea component region forming hole group held between both sides of the sea-island discharge hole group.
 34. The composite spinneret according to claim 30, wherein the composite spinneret is used for production of a multicomponent fiber including a sea component and an island component, wherein, in cross-section observation of the multicomponent fiber, the multicomponent fiber includes: a sea-island region with the plurality of island components arranged in the sea component; and one or more sea component regions formed only of the sea component between the sea-island region, and width (H) of the sea component region is larger than the maximum value of distance (W) between island components existing in the sea-island region and neighboring each other.
 35. A multicomponent fiber including a sea component and an island component, wherein, in cross-section observation of the multicomponent fiber, the multicomponent fiber includes: a sea-island region with a plurality of island components arranged in the sea component; and more than one sea component region formed only of the sea component between the sea-island region, and a width (H) of the sea component region is larger than a maximum value of a distance (W) between island components existing in the sea-island region and neighboring each other.
 36. The multicomponent fiber according to claim 35, wherein the sea component region extends inwardly from a surface layer of the multicomponent fiber.
 37. The multicomponent fiber according to claim 36, wherein the island components in the sea-island region are regularly arranged.
 38. The multicomponent fiber according to claim 35, wherein, in cross-section observation of the sea-island multicomponent fiber, a ratio (L/D) of a length (L) of the sea component region to a diameter (D) of the multicomponent fiber is 0.25 or more.
 39. The multicomponent fiber according to claim 35, wherein, in cross-section observation of the sea-island multicomponent fiber, the width (H) of the sea component region is larger than the maximum diameter (d) of the island component.
 40. The multicomponent fiber according to claim 39, wherein, in cross-section observation, there exists at least one sea component region where the width (H) of the sea component region is larger than the maximum diameter (d) of the island component, and a length (L1) of the sea component region is equal to or larger than ¼ of the diameter (D) of the multicomponent fiber.
 41. The multicomponent fiber according to claim 40, wherein, in cross-section observation, a cross-section area (Ac) of the multicomponent fiber and a sum of areas (As) of sea component regions satisfy: 0.05≦As/Ac≦0.35. 